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Basics of “C” Programming
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CSE 105 Structured Programming Language (C)
Module 6: Introduction to C Language ITEI102 Introduction to Programming Structure of C++ Program - Programming Terminologies - Microsoft Visual Studio.
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C Programming Lecture PPT
rizvicoe/cplect
Folders and files, repository files navigation, c programming, prof. shiburaj, rizvi college of engineering.
Hello everyone,
These set of pages are the materials used by me for the delivery of the lectures in the course of C Programming.
- Introduction to components of a Computer System
- Introduction to Algorithm and Flowchart
- Keywords, Identifiers, Constants and Variables
- Data types in C
- Operators in C
- Basic Input and Output Operations
- Expressions and Precedence of Operators
- In-built Functions
- Introduction to Control Structures
- If statement, If-else statement, Nested if-else, else-if Ladder
- Switch statement
- For loop, While loop
- Introduction to functions
- Function prototype, Function definition, Accessing a function and parameter passing.
- Introduction to Arrays
- Declaration and initialization of one dimensional and two-dimensional arrays.
- Definition and initialization of String
- String functions
- Concept of Structure and Union
- Declaration and Initialization of structure and union
- Nested structures
- Array of Structures
- Passing structure to functions
- Fundamentals of pointers
- Declaration, initialization and dereferencing of pointers
- Operations on Pointers
- Concept of dynamic memory allocation
Sections of a C Program
C compilers.
- GNU GCC (Link 1) (Link for Windows - Mingw)
- Tiny C Compiler (Link)
- Portable C Compiler (Link)
- CLang (Link)
- Digital Mars Compiler (Link)
IDE for C Programming
- CodeBlocks (http://www.codeblocks.org/)
- Bloodshed Dev C++ (https://www.bloodshed.net)
- Notepad++ (https://notepad-plus-plus.org) (Use NppExec Plugin with Gcc Compiler)
- Visual Studio Comunity Edition (Link)
- Turbo C++ (Link to Website)
GCC Compiler Parameters
- -o name = Set the name of the output file eg: -o test.exe
- -E = Used to return the preprocessor output (.i extention)
- -S = Used to return assembly code (.s extension)
- -C = Used to create the object file (.o extension)
- -save-temps = To generate all the intermediate files during compilation.
- -ansi = To enable the ANSI standard
- -std=c89|c99|c9x = To change the standard
- -pedantic-errors = Strict conformance to ISO standards
- -Wall = Show errors and warnings
- List of C Programs (https://www.faceprep.in/c-programming-questions/)
- List of C Programs Link 2 (https://www.studytonight.com/c/programs/)
C Program Structure (Basic)
C program structure (advanced), contributors 2.
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C is a high-level programming language that was originally developed in the early 1970s for system programming and has since become widely used for a variety of applications. It is a procedural language that allows for structured programming and modular design, making it highly flexible and efficient. C has a rich set of built-in functions and operators, and allows for low-level memory manipulation, making it ideal for applications that require high performance and speed. It has also been widely adopted in the field of embedded systems and microcontrollers. C continues to be an important language for software development today. By using our template, you can convey your message in a clear and concise manner.
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DESCRIPTION
C Programming
Welcome to C!
Course Objectives
Be able to read and write C programs Understand all C language constructs Be able to use pointers Have a good overview of the Standard Library Be aware of some of C’s traps and pitfalls
Practical Exercises
Practical exercises are a very important part of the course
An opportunity to experience some of the traps first hand!
Solutions are provided, discuss these amongst yourselves and/or with the tutor
If you get stuck, ask If you can’t understand one of the solutions, ask If you have an alternative solution, say
Features of C
C can be thought of as a “high level assembler” Designed for maximum processor speed Safety a definite second! THE system programming language (Reasonably) portable Has a “write only” reputation
History of C
Developed by Brian Kernighan and Dennis Ritchie of AT&T Bell Labs in 1972
In 1983 the American National Standards Institute began the standardisation process
In 1989 the International Standards Organisation continued the standardisation process
In 1990 a standard was finalised, known simply as “Standard C”
Everything before this is known as “K&R C”
Standard C vs K&R C
Parameter type checking added Proper floating point support added Standard Library covered too Many “grey areas” addressed New features added
Standard C is now the choice All modern C compilers are Standard C The course discusses Standard C
A C Program
#include <stdio.h> /* comment */
int main(void){
printf("Hello\n");printf("Welcome to the Course!\n");
HelloWelcome to the Course!
tells compiler about standard input and output functions (i.e. printf + others)
main function
flag success to operating system
The Format of C
Statements are terminated with semicolons Indentation is ignored by the compiler C is case sensitive - all keywords and Standard
Library functions are lowercase Strings are placed in double quotes Newlines are handled via \n Programs are capable of flagging success or
error, those forgetting to do so have one or other chosen randomly!
Another Example
#include <stdio.h>
printf("Enter two numbers: ");scanf("%i %i", &a, &b);
printf("%i - %i = %i\n", a, b, a - b);
create two integer variables, “a” and “b”
read two integer numbers into “a”
write “a”, “b” and “a-b” in the format specified
Enter two numbers: 21 1721 - 17 = 4
Variables must be declared before use immediately after “{”
Valid characters are letters, digits and “_” First character cannot be a digit 31 characters recognised for local variables
(more can be used, but are ignored) Some implementations recognise only 6
characters in global variables (and function names)!
Upper and lower case letters are distinct
printf and scanf
printf writes integer values to screen when %i is used
scanf reads integer values from the keyboard when %i is used
“&” VERY important with scanf (required to change the parameter, this will be investigated later) - absence will make program very ill
“&” not necessary with printf because current value of parameter is used
Integer Types in C
C supports different kinds of integers maxima and minima defined in “limits.h”
type format bytes minimum maximum
char %c 1 CHAR_MIN CHAR_MAX
signed char %c 1 SCHAR_MIN SCHAR_MAX
unsigned char %c 1 0 UCHAR_MAX
short [int] %hi 2 SHRT_MIN SHRT_MAX
unsigned short %hu 2 0 USHRT_MAX
int %i 2 or 4 INT_MIN INT_MAX
unsigned int %u 2 or 4 0 UINT_MAX
long [int] %li 4 LONG_MIN LONG_MAX
unsigned long %lu 4 0 ULONG_MAX
Integer Example
#include <stdio.h>#include <limits.h>
unsigned long big = ULONG_MAX;
printf("minimum int = %i, ", INT_MIN);printf("maximum int = %i\n", INT_MAX);printf("maximum unsigned = %u\n", UINT_MAX);printf("maximum long int = %li\n", LONG_MAX);printf("maximum unsigned long = %lu\n", big);
return 0;} minimum int = -32768, maximum int = 32767
maximum unsigned = 65535maximum long int = 2147483647maximum unsigned long = 4294967295
minimum int = -32768, maximum int = 32767maximum unsigned = 65535maximum long int = 2147483647maximum unsigned long = 4294967295
Character Example
char lower_a = 'a';char lower_m = 'm';
printf("minimum char = %i, ", CHAR_MIN);printf("maximum char = %i\n", CHAR_MAX);
printf("after '%c' comes '%c'\n", lower_a, lower_a + 1);printf("uppercase is '%c'\n", lower_m - 'a' + 'A');
return 0;} minimum char = 0, maximum char = 255
after 'a' comes 'b'uppercase is 'M'
minimum char = 0, maximum char = 255after 'a' comes 'b'uppercase is 'M'
Note: print integer value of character
Integers With Different Bases
It is possible to work in octal (base 8) and hexadecimal (base 16)
int dec = 20, oct = 020, hex = 0x20;
printf("dec=%d, oct=%d, hex=%d\n", dec, oct, hex);printf("dec=%d, oct=%o, hex=%x\n", dec, oct, hex);
dec=20, oct=16, hex=32dec=20, oct=20, hex=20
zero puts compiler into octal mode!
zero “x” puts compiler into hexadecimal
Real Types In C
C supports different kinds of reals maxima and minima are defined in “float.h”
float %f %e %g 4 FLT_MIN FLT_MAX
double %lf %le %lg 8 DBL_MIN DBL_MAX
long double %Lf %Le %Lg 10 LDBL_MIN LDBL_MAX
Real Example
#include <stdio.h>#include <float.h>
double f = 3.1416, g = 1.2e-5, h = 5000000000.0;
printf("f=%lf\tg=%lf\th=%lf\n", f, g, h);printf("f=%le\tg=%le\th=%le\n", f, g, h);printf("f=%lg\tg=%lg\th=%lg\n", f, g, h);
printf("f=%7.2lf\tg=%.2le\th=%.4lg\n", f, g, h);
f=3.141600 g=0.000012 h=5000000000.000000f=3.141600e+00 g=1.200000e-05 h=5.000000e+09f=3.1416 g=1.2e-05 h=5e+09f= 3.14 g=1.20e-05 h=5e+09
Constants have types in C Numbers containing “.” or “e” are double: 3.5,
1e-7, -1.29e15 For float constants append “F”: 3.5F, 1e-7F For long double constants append “L”: -
1.29e15L, 1e-7L Numbers without “.”, “e” or “F” are int, e.g.
10000, -35 (some compilers switch to long int if the constant would overflow int)
For long int constants append “L”, e.g. 9000000L
double f = 5000000000.0;double g = 5000000000;
printf("f=%lf\n", f);printf("g=%lf\n", g);
f=5000000000.000000g=705032704.000000
double constant created because of “.”
constant is int or long but 2,147,483,647 is the
Named Constants
Named constants may be created using const
const long double pi = 3.141592653590L;const int days_in_week = 7;const sunday = 0;
days_in_week = 5;
creates an integer
Preprocessor Constants
Named constants may also be created using the Preprocessor– Needs to be in “search and replace” mode
– Historically these constants consist of capital letters
#define PI 3.141592653590L#define DAYS_IN_WEEK 7#define SUNDAY 0
int day = SUNDAY;long flag = USE_API;
search for “PI”, replace with 3.1415....
“PI” is NOT substituted here
Note: no “=” and no “;”
Take Care With printf And scanf!
short a = 256, b = 10;
printf("Type a number: ");scanf("%c", &a);
printf("a = %hi, b = %f\n", a, b);
“%c” fills one byte of “a” which is two
bytes in size
“%f” expects 4 byte float in IEEE format, “b” is 2 bytes and
NOT in IEEE format
Type a number: 1a = 305 b = Floating support not loaded
K&R C vs Standard C main, printf Variables Integer types Real types Constants Named constants Preprocessor constants Take care with printf and scanf
Operators in C
Arithmetic operators Cast operator Increment and Decrement Bitwise operators Comparison operators Assignment operators sizeof operator Conditional expression operator
Arithmetic Operators
C supports the arithmetic operators:
- subtraction
* multiplication
% modulo (remainder)
“%” may not be used with reals
Using Arithmetic Operators
The compiler uses the types of the operands to determine how the calculation should be done
int i = 5, j = 4, k;double f = 5.0, g = 4.0, h;
k = i / j;h = f / g;h = i / j;
“i” and “j” are ints, integer division is done, 1 is
assigned to “k”
“f” and “g” are double, double division is done, 1.25
is assigned to “h”
integer division is still done, despite “h” being double. Value assigned is 1.00000
The Cast Operator
The cast operator temporarily changes the type of a variable
int i = 5, j = 4;double f;
f = (double)i / j;f = i / (double)j;f = (double)i / (double)j;f = (double)(i / j);
integer division is done here, the result, 1, is changed to a
double, 1.00000
if either operand is a double, the other is automatically
Increment and Decrement
C has two special operators for adding and subtracting one from a variable
++ increment
- - decrement
These may be either prefix (before the variable) or postfix (after the variable):
int i = 5, j = 4;
i++;--j;++i;
“i” becomes 6
“j” becomes 3
“i” becomes 7
Prefix and Postfix
The prefix and postfix versions are different
int i, j = 5;
i = ++j;printf("i=%d, j=%d\n", i, j);
j = 5;i = j++;printf("i=%d, j=%d\n", i, j);
return 0;} i=6, j=6
i=6, j=6i=5, j=6
equivalent to: 1. j++; 2. i = j;
equivalent to: 1. i = j; 2. j++;
To understand C’s comparison operators (less than, greater than, etc.) and the logical operators (and, or, not) it is important to understand how C regards truth
There is no boolean data type in C, integers are used instead
The value of 0 (or 0.0) is false Any other value, 1, -1, 0.3, -20.8, is true
if(32)printf("this will always be printed\n");
if(0)printf("this will never be printed\n");
Comparison Operators
C supports the comparison operators:
< less than
<= less than or equal to
> greater than
>= greater than or equal to
== is equal to
!= is not equal to
These all give 1 (non zero value, i.e. true) when the comparison succeeds and 0 (i.e. false) when the comparison fails
Logical Operators
C supports the logical operators:
&& and
These also give 1 (non zero value, i.e. true) when the condition succeeds and 0 (i.e. false) when the condition fails
int i, j = 10, k = 28;
i = ((j > 5) && (k < 100)) || (k > 24);
Logical Operator Guarantees
C makes two important guarantees about the evaluation of conditions
Evaluation is left to right Evaluation is “short circuit”
if(i < 10 && a[i] > 0)printf("%i\n", a[i]);
“i < 10” is evaluated first, if false the whole statement is false (because false AND anything is false) thus “a[i] > 0”
would not be evaluated
Remember to use parentheses with conditions, otherwise your program may not mean what you think
int i = 10;
if(!i == 5)printf("i is not equal to five\n");
elseprintf("i is equal to five\n");
in this attempt to say “i not equal to five”, “!i” is evaluated first. As “i” is 10, i.e. non zero, i.e. true, “!i” must be false, i.e. zero. Zero is
compared with five
i is equal to fivei is equal to five
Bitwise Operators
C has the following bit operators which may only be applied to integer types:
& bitwise and
| bitwise inclusive or
^ bitwise exclusive or
~ one’s compliment
>> right shift
<< left shift
Bitwise Example
short a = 0x6eb9;short b = 0x5d27;unsigned short c = 7097;
printf("0x%x, ", a & b);printf("0x%x, ", a | b);printf("0x%x\n", a ^ b);
printf("%u, ", c << 2);printf("%u\n", c >> 1);
0x4c21, 0x7fbf, 0x339e28388, 3548
0x6eb9 0110 1110 1011 10010x5d27 0101 1101 0010 01110x4c21 0100 1100 0010 0001
0x6eb9 0110 1110 1011 10010x5d27 0101 1101 0010 01110x7fbf 0111 1111 1011 1111
0x6eb9 0110 1110 1011 10010x5d27 0101 1101 0010 01110x339e 0011 0011 1001 1110
7097 0001 1011 1011 100128388 0110 1110 1110 0100
7097 0001 1011 1011 1001 3548 0000 1101 1101 1100
Assignment is more flexible than might first appear
An assigned value is always made available for subsequent use
int i, j, k, l, m, n;
i = j = k = l = m = n = 22;
printf("%i\n", j = 93);
“n = 22” happens first, this makes 22 available for assignment to “m”. Assigning 22 to “m” makes 22 available for assignment to “l” etc.
“j” is assigned 93, the 93 is then made available to printf for printing
One of the most frequent mistakes is to confuse test for equality, “==”, with assignment, “=”
if(i = 0)printf("i is equal to zero\n");
elseprintf("somehow i is not zero\n");
somehow i is not zerosomehow i is not zero
Other Assignment Operators
There is a family of assignment operators:
+= -= *= /= %=
&= |= ^=
<<= >>=
In each of these:
expression1 op= expression2
is equivalent to:
(expression1) = (expression1) op (expression2)
a += 27;a += 27;
a = a + 27;a = a + 27;
f /= 9.2;f /= 9.2;
f = f / 9.2;f = f / 9.2;
i *= j + 2;i *= j + 2;
i = i * (j + 2);i = i * (j + 2);
sizeof Operator
C has a mechanism for determining how many bytes a variable occupies
printf("\"big\" is %u bytes\n", sizeof(big));printf("a short is %u bytes\n", sizeof(short));printf("a double is %u bytes\n", sizeof double);
"big" is 4 bytesa short is 2 bytesa double is 8 bytes
Conditional Expression Operator
The conditional expression operator provides an in-line if/then/else
If the first expression is true, the second is evaluated
If the first expression is false, the third is evaluated
int i, j = 100, k = -1;
i = (j > k) ? j : k;
i = (j < k) ? j : k;
if(j > k)i = j;
if(j < k)i = j;
Precedence of Operators
C treats operators with different importance, known as precedence
There are 15 levels In general, the unary operators have higher
precedence than binary operators Parentheses can always be used to improve
clarity#include <stdio.h>
int j = 3 * 4 + 48 / 7;
printf("j = %i\n", j);
j = 18j = 18
Associativity of Operators
For two operators of equal precedence (i.e. same importance) a second rule, “associativity”, is used
Associativity is either “left to right” (left operator first) or “right to left” (right operator first)
int i = 6 * 4 / 7;
printf("i = %d\n", i);
Precedence/Associativity Table
Associativity() [] -> .
left to right
! ~ ++ -- - + (cast) * & sizeof
right to left
<< >>
< <= >= >
= += -= *= /= %= etc
int i = 0, j, k = 7, m = 5, n;
j = m += 2;printf("j = %d\n", j);
j = k++ > 7;printf("j = %d\n", j);
j = i == 0 & k;printf("j = %d\n", j);
n = !i > k >> 2;printf("n = %d\n", n);
Control Flow
Decisions - if then else More decisions - switch Loops - while, do while, for Keyword break Keyword continue
Decisions - if then
Parentheses surround the test One statement becomes the “then part” If more are required, braces must be used
scanf("%i", &i);
if(i > 0)printf("a positive number was entered\n");
if(i < 0) {printf("a negative number was entered\n");i = -i;
A semicolon after the condition forms a “do nothing” statement
printf("input an integer: ");scanf("%i", &j);
if(j > 0);printf("a positive number was entered\n");
input an integer: -6
a positive number was entered
if then else
An optional else may be added One statement by default, if more are required,
braces must be used
if(i > 0)printf("i is positive\n");
elseprintf("i is negative\n");
else {printf("i is negative\n");i = -i;
Nesting ifs
else associates with the nearest if
int i = 100;
if(i > 0)if(i > 1000)
printf("i is big\n");else
printf("i is reasonable\n");
printf("i is reasonable\n"); i is reasonablei is reasonable
int i = -20;
if(i > 0) {if(i > 1000)
printf("i is big\n");} else
printf("i is negative\n");
printf("i is negative\n");i is negativei is negative
C supports a switch for multi-way decision making
switch(c) { case 'a': case 'A':
printf("area = %.2f\n", r * r * pi);break;
case 'c': case 'C':printf("circumference = %.2f\n", 2 * r * pi);break;
case 'q':printf("quit option chosen\n");break;
default:printf("unknown option chosen\n");break;
More About switch
Only integral constants may be tested If no condition matches, the default is executed If no default, nothing is done (not an error) The break is important
switch(f) { case 2:
switch(i) { case 2 * j:
switch(i) { case 3: printf("i = 3\n"); case 2: printf("i = 2\n"); case 1: printf("i = 1\n");}
i = 3i = 2i = 1
A switch Example
printf("On the ");switch(i) { case 1: printf("1st"); break; case 2: printf("2nd"); break; case 3: printf("3rd"); break; default: printf("%ith", i); break;}printf(" day of Christmas my true love sent to me ");switch(i) { case 12: printf("twelve lords a leaping, "); case 11: printf("eleven ladies dancing, "); case 10: printf("ten pipers piping, "); case 9: printf("nine drummers drumming, "); case 8: printf("eight maids a milking, "); case 7: printf("seven swans a swimming, "); case 6: printf("six geese a laying, "); case 5: printf("five gold rings, "); case 4: printf("four calling birds, "); case 3: printf("three French hens, "); case 2: printf("two turtle doves and "); case 1: printf("a partridge in a pear tree\n");}
The simplest C loop is the while Parentheses must surround the condition One statement forms the body of the loop Braces must be added if more statements are to
be executed
while(j > 0)printf("j = %i\n", j--);
j = 5j = 4j = 3j = 2j = 1
j = 5j = 4j = 3j = 2j = 1while(j > 0) {
printf("j = %i\n", j);j--;
while(j > 0) {printf("j = %i\n", j);j--;
(Another) Semicolon Warning!
A semicolon placed after the condition forms a body that does nothing
while(j > 0);printf("j = %i\n", j--);
program disappears into an infinite loop
• Sometimes an empty loop body is required
while(scanf("%i", &j) != 1)while((c = getchar()) != '\n')
placing semicolon on the line below
makes the intention obvious
while, Not Until!
Remember to get the condition the right way around!
printf("start\n");while(j == 0)
printf("j = %i\n", j--);printf("end\n");
user probably intends “until j is
equal to zero”, however this is NOT
the way to write itstartend
do while guarantees execution at least once
printf("start\n");do
printf("j = %i\n", j--);while(j > 0);printf("stop\n");
startj = 5j = 4j = 3j = 2j = 1stop
int j = -10;
printf("start\n");do {
} while(j > 0);printf("stop\n");
startj = -10stop
for encapsulates the essential elements of a loop into one statement
for(initial-part; while-condition; update-part)body;
for(j = 5; j > 0; j--)printf("j = %i\n", j);
for(j = 5; j > 0; j--) {printf("j = %i ", j);printf("%s\n", ((j%2)==0)?"even":"odd");
j = 5 oddj = 4 evenj = 3 oddj = 2 evenj = 1 odd
for Is Not Until Either!
Remember to get the for condition the right way around (it is really a while condition)
printf("start\n");for(j = 5; j == 0; j--)
printf("j = %i\n", j);printf("end\n");
the way to write it either!
Stepping With for
Unlike some languages, the for loop is not restricted to stepping up or down by 1
#include <math.h>
double angle;
for(angle = 0.0; angle < 3.14159; angle += 0.2)printf("sine of %.1lf is %.2lf\n",
angle, sin(angle));
Extending the for Loop
The initial and update parts may contain multiple comma separated statements
int i, j, k;
for(i = 0, j = 5, k = -1; i < 10; i++, j++, k--)
The initial, condition and update parts may contain no statements at all!
for(; i < 10; i++, j++, k--)for(; i < 10; i++, j++, k--)
for(;i < 10;)for(;i < 10;)
for(;;)for(;;)
use of a while loop would be clearer here!
creates an infinite loop
The break keyword forces immediate exit from the nearest enclosing loop
Use in moderation!
for(;;) {printf("type an int: ");if(scanf("%i", &j) == 1)
break;while((c = getchar()) != '\n')
;}printf("j = %i\n", j);
;}printf("j = %i\n", j); type an int: an int
type an int: notype an int: 16j = 16
type an int: an inttype an int: notype an int: 16j = 16
if scanf returns 1, jump out of the loop
The continue keyword forces the next iteration of the nearest enclosing loop
for(j = 1; j <= 10; j++) {if(j % 3 == 0)
continue;printf("j = %i\n", j);
j = 1j = 2j = 4j = 5j = 7j = 8j = 10
if j is exactly divisible by 3, skip
if (then) else - watch the semicolons switch can test integer values while, do while, for - watch the semicolons
again break continue
Rules of functions Examples - writing a function, calling a function Function prototypes Visibility Call by value The stack auto, static and register
A function may accept as many parameters as it needs, or no parameters (like main)
A function may return either one or no values Variables declared inside a function are only
available to that function, unless explicitly passed to another function
Writing a Function - Example
int print_table(double start, double end, double step){
double d;int lines = 1;
printf("Celsius\tFarenheit\n");for(d = start; d <= end; d += step, lines++)
printf("%.1lf\t%.1lf\n", d, d * 1.8 + 32);
return lines;}
accept 3 doubles when called
this is the TYPE of the value handed back
this is the ACTUAL value handed back
Calling a Function - Example
int print_table(double, double, double);
int how_many;double end = 100.0;
how_many = print_table(1.0, end, 3);print_table(end, 200, 15);
IMPORTANT: this tells the compiler how print_table works
the compiler knows these should be doubles and
converts them automatically
here the function’s return value is ignored - this is ok, if you don’t want it, you don’t have to use it
Calling a Function - Disaster!
now the compiler does not know how the function works
the compiler does NOT convert these ints to
doubles. The function picks up doubles
The (optional) line
is known as a prototype If the compiler meets a call to an unknown
function it “guesses”– Guess 1: the function returns an int, even if it doesn’t
– Guess 2: you have passed the correct number of parameters and made sure they are all of the correct type, even if you haven’t
The prototype provides the compiler with important information about the return type and parameters
Prototyping is Not Optional
To achieve working programs the compiler is best given a prototype for each function called
When calling a Standard Library function, #include the file specified in the help page(s) - this file will contain the prototype
When calling one of your own functions, write a prototype by hand
Writing Prototypes
int print_table(double, double, double);int print_table(double, double, double);
Function header:
The function prototype may optionally include variable names (which are ignored)
int print_table(double start, double end, double step);int print_table(double start, double end, double step);
int print_table(double x, double y, double z);int print_table(double x, double y, double z);
Take Care With Semicolons
The prototype has a semicolon
The function header has an open brace
Don’t confuse the compiler by adding a semicolon into the function header!
int print_table(double start, double end, double step);{
Example Prototypes
/* no parameters, int return value */int get_integer(void);
/* no parameters, double return value */double get_double(void);
/* no parameters, no return value */void clear_screen(void);
/* three int parameters, int return value */int day_of_year(int day, int month, int year);
/* three int parameters, long int return value */long day_since_1_jan_1970(int, int, int);
/* parameter checking DISABLED, double return value */double k_and_r_function();
/* short int parameter, (default) int return value */transfer(short int s);
Example Calls
int i;double d;long l;short int s = 5;
i = get_integer();
d = get_double();
clear_screen();
i = day_of_year(16, 7, 1969);
l = day_since_1_jan_1970(1, 4, 1983);
d = k_and_r_function();d = k_and_r_function(19.7);d = k_and_r_function("hello world");
i = transfer(s);
the compiler cannot tell which of these (if any) is correct - neither can we
without resorting to documentation!
no mention of “void” when calling these
Rules of Visibility
C is a block structured language, variables may only be used in functions declaring them
int i = 5, j, k = 2;float f = 2.8F, g;
void func(int v){
double d, e = 0.0, f;
i++; g--;f = 0.0;
}func’s “f” is used,
compiler does not know about “d”
“i” and “g” not available here
Call by Value
When a function is called the parameters are copied - “call by value”
The function is unable to change any variable passed as a parameter
In the next chapter pointers are discussed which allow “call by reference”
We have already had a sneak preview of this mechanism with scanf
Call by Value - Example
void change(int v);
int var = 5;
change(var);
printf("main: var = %i\n", var);
void change(int v){
v *= 100;printf("change: v = %i\n", v);
}change: v = 500main: var = 5
change: v = 500main: var = 5
the function was not able to alter “var”
the function is able to alter “v”
C and the Stack
C uses a stack to store local variables (i.e. those declared in functions), it is also used when passing parameters to functions
The calling function pushes the parameters The function is called The called function picks up the parameters The called function pushes its local variables When finished, the called function pops its local
variables and jumps back to the calling function The calling function pops the parameters The return value is handled
Stack Example
double power(int, int);
int x = 2;double d;
d = power(x, 5);printf("%lf\n", d);
double power(int n, int p){
double result = n;
while(--p > 0)result *= n;
return result;}
power: result32.0
C stores local variables on the stack Global variables may be declared. These are not
stack based, but are placed in the data segment Special keywords exist to specify where local
variables are stored:
auto - place on the stack (default)
static - place in the data segment
register - place in a CPU register
Data may also be placed on the heap, this will be discussed in a later chapter
Local variables are automatically allocated on entry into, and automatically deallocated on exit from, a function
These variables are therefore called “automatic” Initial value: random Initialisation: recommended
int table(void){
int lines = 13;auto int columns;
auto keyword redundant
The static keyword instructs the compiler to place a variable into the data segment
The data segment is permanent (static) A value left in a static in one call to a function
will still be there at the next call Initial value: 0 Initialisation: unnecessary if you like zeros
int running_total(void){
static int rows;
permanently allocated, but local to this
The register keyword tells the compiler to place a variable into a CPU register (you cannot specify which)
If a register is unavailable the request will be ignored
Largely redundant with optimising compilers Initial value: random Initialisation: recommended
void speedy_function(void){
register int i;
for(i = 0; i < 10000; i++)
Global Variables
Global variables are created by placing the declaration outside all functions
They are placed in the data segment Initial value: 0 Initialisation: unnecessary if you like zeros
variable “d” is global and available to all functions defined
Writing and calling functions The need for function prototypes Visibility C is “call by value” Local variables are stack based, this can be
changed with the static and register keywords
Global variables may be created, they are stored in the data segment
Declaring pointers The “&” operator The “*” operator Initialising pointers Type mismatches Call by reference Pointers to pointers
Pointers - Why?
Using pointers allows us to:– Achieve call by reference (i.e. write functions which change
their parameters)
– Handle arrays efficiently
– Handle structures (records) efficiently
– Create linked lists, trees, graphs etc.
– Put data onto the heap
– Create tables of functions for handling Windows events, signals etc.
Already been using pointers with scanf Care must be taken when using pointers since
there are no safety features
Declaring Pointers
Pointers are declared by using “*” Declare an integer:
int i;int i;
Declare a pointer to an integer:
int *p;int *p;
There is some debate as to the best position of the “*”
int* p;int* p;
Example Pointer Declarations
int *pi; /* pi is a pointer to an int */
long int *p; /* p is a pointer to a long int */
float* pf; /* pf is a pointer to a float */
char c, d, *pc; /* c and d are a char pc is a pointer to char */
double* pd, e, f; /* pd is pointer to a double e and f are double */
char* start; /* start is a pointer to a char */
char* end; /* end is a pointer to a char */
The “&” Operator
The “&”, “address of” operator, generates the address of a variable
All variables have addresses except register variables
char g = 'z';
char c = 'a';char *p;
p = &c;p = &g;
'a'0x11320x1132
'z'0x91A20x91A2
Pointers may only point to variables of the same type as the pointer has been declared to point to
A pointer to an int may only point to an int– not to char, short int or long int, certainly not to float,
double or long double
A pointer to a double may only point to a double– not to float or long double, certainly not to char or any of
the integers
int *p; /* p is a pointer to an int */long large = 27L; /* large is a long int,
initialised with 27 */
p = &large; /* ERROR */
The “*” Operator
The “*”, “points to” operator, finds the value at the end of a pointer
p = &c;printf("%c\n", *p);
p = &g;printf("%c\n", *p);
return 0;} a
print “what p points to”
Writing Down Pointers
It is not only possible to read the values at the end of a pointer as with:
It is possible to write over the value at the end of a pointer:
p = &c;*p = 'b';printf("%c\n", *p);
make what p points to equal to ‘b’
Initialisation Warning!
The following code contains a horrible error:
short i = 13;short *p;
*p = 23;printf("%hi\n", *p);
Initialise Pointers!
Pointers are best initialised! A pointer may be declared and initialised in a
single step
short i = 13;short *p = &i;
This does NOT mean “make what p points to equal to the address of i”
It DOES mean “declare p as a pointer to a short int, make p equal to the address of i”
short *p = &i;short *p = &i; short *p = &i;short *p = &i;
short *p = &i;short *p = &i;
A special invalid pointer value exists #defined in various header files, called NULL
When assigned to a pointer, or when found in a pointer, it indicates the pointer is invalid
short i = 13;short *p = NULL;
if(p == NULL)printf("the pointer is invalid!\n");
elseprintf("the pointer points to %hi\n", *p);
A World of Difference!
There is a great deal of difference between:
int i = 10, j = 14;int *p = &i;int *q = &j;
100x15A00x15A0
0x15A40x15A4
Fill in the Gaps
int i = 10, j = 14, k;int *p = &i;int *q = &j;
p = &k;
Type Mismatch
The compiler will not allow type mismatches when assigning to pointers, or to where pointers point
p = *q;*p = q;
cannot write 0x15A4 into i cannot write
Call by Value - Reminder
Call by Reference
void change(int* p);
change(&var);
void change(int* p){
*p *= 100;printf("change: *p = %i\n", *p);
change: *p = 500main: var = 500
prototype “forces” us to pass a pointer
Pointers to Pointers
C allows pointers to any type It is possible to declare a pointer to a pointer
int i = 16;int *p = &i;int **pp;
pp = &p;printf("%i\n", **pp);
pp is a “pointer to” a “pointer to an int”
int i = 10, j = 7, k;int *p = &i;int *q = &j;int *pp = &p;
*pp = &k;
i = *q***pp;
i = *q/**pp; /* headache? */;
Arrays in C
Declaring arrays Accessing elements Passing arrays into functions Using pointers to access arrays Strings The null terminator
Declaring Arrays
An array is a collection of data items (called elements) all of the same type
It is declared using a type, a variable name and a CONSTANT placed in square brackets
C always allocates the array in a single block of memory
The size of the array, once declared, is fixed forever - there is no equivalent of, for instance, the “redim” command in BASIC
#define SIZE 10int a[5]; /* a is an array of 5 ints */long int big[100]; /* big is 400 bytes! */double d[100]; /* but d is 800 bytes! */long double v[SIZE]; /* 10 long doubles, 100 bytes */
int a[5] = { 10, 20, 30, 40, 50 };double d[100] = { 1.5, 2.7 };short primes[] = { 1, 2, 3, 5, 7, 11, 13 };long n[50] = { 0 };
int i = 7;const int c = 5;
int a[i];double d[c];short primes[];
all five elements initialised
first two elements initialised,
remaining ones set to zero
compiler fixes size at 7 elements
quickest way of settingALL elements to zero
Accessing Elements
The elements are accessed via an integer which ranges from 0..size-1
There is no bounds checking
int a[6];int i = 7;
a[0] = 59;a[5] = -10;a[i/2] = 2;
a[6] = 0;a[-1] = 5;
Array Names
There is a special and unusual property of array names in C
The name of an array is a pointer to the start of the array, i.e. the zeroth element, thus
a == &a[0]
int a[10];int *p;
float f[5]float *fp;
p = a; /* p = &a[0] */
fp = f; /* fp = &f[0] */
Passing Arrays to Functions
When an array is passed to a function a pointer to the zeroth element is passed across
The function may alter any element The corresponding parameter may be declared as
a pointer, or by using the following special syntax
int add_elements(int a[], int size){
int add_elements(int *p, int size){
void sum(long [], int);
long primes[6] = { 1, 2,3, 5, 7, 11 };
sum(primes, 6);
printf("%li\n", primes[0]);
void sum(long a[], int sz){
int i;long total = 0;
for(i = 0; i < sz; i++)total += a[i];
a[0] = total;}
the total is written over element zero
provides bounds checking
Using Pointers
Pointers may be used to access array elements rather than using constructs involving “[ ]”
Pointers in C are automatically scaled by the size of the object pointed to when involved in arithmetic
long v[6] = { 1,2, 3,4,5,6 };
p = v;printf("%ld\n", *p);p++;printf("%ld\n", *p);p += 4;printf("%ld\n", *p);
1000 1 2 3 4 5 6
Pointers Go Backwards Too
Scaling not only happens when addition is done, it happens with subtraction too
p = v + 5;printf("%ld\n", *p);p--;printf("%ld\n", *p);p -= 2;printf("%ld\n", *p);
1020 1 2 3 4 5 6
Pointers May be Subtracted
When two pointers into the same array are subtracted C scales again, giving the number of array elements separating them
double d[7] = { 1.1, 2.2,3.3, 4.4, 5.5, 6.6, 7.7 };
double *p1;double *p2;
p1 = d + 1;p2 = d + 6;
printf("%i\n", p2 - p1);
1.1 2.2 3.3 4.4 5.5 6.6 7.7
2016 2032 20482024 2040
Using Pointers - Example
long sum(long*, int);
printf("%li\n", sum(primes, 6));
long sum(long *p, int sz){
long *end = p + sz;long total = 0;
while(p < end)total += *p++;
return total;}
*p++ means:*p++ find the value at the end of the pointer*p++ increment the POINTER to point to the
next element(*p)++ means:
(*p)++ find the value at the end of the pointer(*p)++ increment the VALUE AT THE END OF THE POINTER (the pointer never moves)
*++p means:*++p increment the pointer*++p find the value at the end of the pointer
Which Notation?
An axiom of C states a[i] is equivalent to *(a + i)
short a[8] = { 10, 20, 30, 40, 50, 60, 70, 80 };short *p = a;
printf("%i\n", a[3]);printf("%i\n", *(a + 3));printf("%i\n", *(p + 3));printf("%i\n", p[3]);printf("%i\n", 3[a]);
10 20 30 40 50 60 70 80
1000 1004 1008 10121002 1006 1010 1014
C has no native string type, instead we use arrays of char
A special character, called a “null”, marks the end (don’t confuse this with the NULL pointer )
This may be written as ‘\0’ (zero not capital ‘o’) This is the only character whose ASCII value is
zero Depending on how arrays of characters are built,
we may need to add the null by hand, or the compiler may add it for us
char first_name[5] = { 'J', 'o', 'h', 'n', '\0' };
char last_name[6] = "Minor";
char other[] = "Tony Blurt";
char characters[7] = "No null";
'J' 'o' 'h' 'n' 0first_name
'M' 'i' 'n' 'o' 'r'last_name 0
'T' 'o' 'n' 'y' 32other 'B' 'l' 'u' 'r' 't' 0
'N' 'o' 32 'n' 'u'characters 'l' 'l'
this special case specifically excludes the null terminator
Printing Strings
Strings may be printed by hand Alternatively printf supports “%s”
char other[] = "Tony Blurt";char other[] = "Tony Blurt";
p = other;while(*p != '\0')
printf("%c", *p++);printf("\n");
while(other[i] != '\0')printf("%c", other[i++]);
printf("\n");
printf("%s\n", other);printf("%s\n", other);
Null Really Does Mark the End!
printf("%s\n", other);
other[4] = '\0';
return 0;} Tony Blurt
Tony BlurtTony
even though the rest of the data is still there, printf will NOT move past the null terminator
Assigning to Strings
Strings may be initialised with “=”, but not assigned to with “=”
Remember the name of an array is a CONSTANT pointer to the zeroth element
#include <stdio.h>#include <string.h>
char who[] = "Tony Blurt";
who = "John Minor";
strcpy(who, "John Minor");
Pointing to Strings
To save us declaring many character arrays to store strings, the compiler can store them directly in the data segment
We need only declare a pointer The compiler may recycle some of these strings,
therefore we must NOT alter any of the characters
char *p = "Data segment!!";char *q = "nt!!";
'D' 'a' 't' 'a' 32 's' 'e' 'g' 'm' 'e' 'n' 't' '!' '!' 0
0xF100 0xF10A
char *p = "a string in the data segment\n";
"a second string in the data segment\n";
printf("a third string in the data segment\n");
printf("%s", p);
this utterly pointless statement causes the compiler to store the characters, unfortunately we forget to save the address
a third string in the data segmenta string in the data segmenta string in the data segment
Multidimensional Arrays
C does not support multidimensional arrays However, C does support arrays of any type
including arrays of arrays
float rainfall[12][365];float rainfall[12][365]; “rainfall” is an array of 12 arrays of 365 float
short exam_marks[500][10];short exam_marks[500][10]; “exam_marks” is an array of 500 arrays of 10 short int
const int brighton = 7;int day_of_year = 238;
rainfall[brighton][day_of_year] = 0.0F;
int i;int a[10];
for(i = 0; i <= 10; i++) {printf("%d\n", i);a[i] = 0;
How many times does the following program loop?
Arrays are declared with a type, a name, “[ ]” and a CONSTANT
Access to elements by array name, “[ ]” and an integer
Arrays passed into functions by pointer Pointer arithmetic Strings - arrays of characters with a null
terminator Sometimes compiler stores null for us (when
double quotes are used) otherwise we have to store it ourselves
Structures in C
Concepts Creating a structure template Using the template to create an instance Initializing an instance Accessing an instance’s members Passing instances to functions Linked lists
A structure is a collection of one of more variables grouped together under a single name for convenient handling
The variables in a structure are called members and may have any type, including arrays or other structures
The steps are:– set-up a template (blueprint) to tell the compiler how to build
the structure
– Use the template to create as many instances of the structure as desired
– Access the members of an instance as desired
Setting up the Template
Structure templates are created by using the struct keyword
struct Book{
char title[80];char author[80];float price;char isbn[20];
struct Date{
int day;int month;int year;
struct Library_member{
char name[80];char address[200];long member_number;float fines[10];struct Date dob;struct Date enrolled;
struct Library_book{
struct Book b;struct Date due;struct Library_member *who;
Creating Instances
Having created the template, an instance (or instances) of the structure may be declared
} today, tomorrow;
struct Date next_monday;
struct Date next_week[7];
an array of 7 date instances
instances must be declared before the ‘;’ ...
... or “struct Date” has to be repeated
Initialising Instances
Structure instances may be initialised using braces (as with arrays)
int primes[7] = { 1, 2, 3, 5, 7, 11, 13 };
struct Date bug_day = { 1, 1, 2000 };
struct Book k_and_r = {"The C Programming Language 2nd edition","Brian W. Kernighan and Dennis M. Ritchie",31.95,"0-13-110362-8"
}; struct Book{
Structures Within Structures
struct Library_member m = {"Arthur Dent","16 New Bypass",42,{ 0.10, 2.58, 0.13, 1.10 },{ 18, 9, 1959 },{ 1, 4, 1978 }
initialises first 4 elements of array “fines”, remainder are initialised to 0.0
initialises day, month and year of “dob”
initialises day, month and year of “enrolled”
Accessing Members
Members are accessed using the instance name, “.” and the member name
printf("name = %s\n", m.name);printf("membership number = %li\n", m.member_number);
printf("fines: ");for(i = 0; i < 10 && m.fines[i] > 0.0; i++)
printf("£%.2f ", m.fines[i]);
printf("\njoined %i/%i/%i\n", m.enrolled.day,m.enrolled.month, m.enrolled.year);
struct Library_member m;struct Library_member m;
Unusual Properties
Structures have some very “un-C-like” properties, certainly when considering how arrays are handled
Arrays Structures
Name is pointer to the structure itselfzeroth element
Passed to functions by pointer value or pointer
Returned from functions no way by value or pointer
May be assigned with “=” no way yes
Instances may be Assigned
Two structure instances may be assigned to one another via “=”
All the members of the instance are copied (including arrays or other structures)
struct Library_member m = {"Arthur Dent",.....
};struct Library_member tmp;
copies array “name”, array “address”, long integer “member_number”, array “fines”, Date structure “dob” and Date structure “enrolled”
Passing Instances to Functions
An instance of a structure may be passed to a function by value or by pointer
Pass by value becomes less and less efficient as the structure size increases
Pass by pointer remains efficient regardless of the structure size
void by_value(struct Library_member);void by_reference(struct Library_member *);
by_value(m);by_reference(&m);
compiler writes a pointer (4 bytes?) onto the stack
compiler writes 300+ bytes onto the stack
Pointers to Structures
Passing pointers to structure instances is more efficient
Dealing with an instance at the end of a pointer is not so straightforward!
void member_display(struct Library_member *p){
printf("name = %s\n", (*p).name);printf("membership number = %li\n", (*p).member_number);
printf("fines: ");for(i = 0; i < 10 && (*p).fines[i] > 0.0; i++)
printf("£%.2f ", (*p).fines[i]);
printf("\njoined %i/%i/%i\n", (*p).enrolled.day,(*p).enrolled.month, (*p).enrolled.year);
Why (*p).name ?
The messy syntax is needed because “.” has higher precedence than “*”, thus:
means “what p.name points to” (a problem because there is no structure instance “p”)
As Kernighan and Ritchie foresaw pointers and structures being used frequently they invented a new operator
p->name = (*p).name
Using p->name
Now dealing with the instance at the end of the pointer is more straightforward
printf("name = %s\n", p->name);printf("address = %s\n", p->address);printf("membership number = %li\n", p->member_number);
printf("fines: ");for(i = 0; i < 10 && p->fines[i] > 0.0; i++)
printf("£%.2f ", p->fines[i]);
printf("\njoined %i/%i/%i\n", p->enrolled.day,p->enrolled.month, p->enrolled.year);
Pass by Reference - Warning
Although pass by reference is more efficient, the function can alter the structure (perhaps inadvertently)
Use a pointer to a constant structure instead
printf("fines: ");for(i = 0; i < 10 && p->fines[i] = 0.0; i++)
printf("£%.2f ", p->fines[i]);}
void member_display(const struct Library_member *p){
function alters the library member instance
Returning Structure Instances
Structure instances may be returned by value from functions
This can be as inefficient as with pass by value Sometimes it is convenient!
struct Complex add(struct Complex a, struct Complex b){
struct Complex result = a;
result.real_part += b.real_part;result.imag_part += b.imag_part;
return result;} struct Complex c1 = { 1.0, 1.1 };
struct Complex c2 = { 2.0, 2.1 };struct Complex c3;
c3 = add(c1, c2); /* c3 = c1 + c2 */
struct Complex c1 = { 1.0, 1.1 };struct Complex c2 = { 2.0, 2.1 };struct Complex c3;
Linked Lists
A linked list node containing a single forward pointer may be declared as follows
struct Node {int data; /* or whatever */struct Node *next_in_line;
pointer to next Node structure
A linked list node containing a forward and a backward pointer may be declared as follows
struct Node {int data;struct Node *next_in_line;struct Node *previous_in_line;
};pointer to previous Node structure
struct Node {char name[10];struct Node *next_in_line;
struct Node a1 = { "John", NULL };struct Node a2 = { "Harriet", &a1 },struct Node a3 = { "Claire", &a2 }struct Node a4 = { "Tony", &a3 };
0x1020 0x102E 0x1032 NULL
Printing the List
The list may be printed with the following code:
struct Node * current = &a4;
while(current != NULL) {printf("%s\n", current->name);current = current->next_in_line;
Creating structure templates using struct Creating and initialising instances Accessing members Passing instances to functions by value and by
reference A new operator: “->” Return by value Linked lists
Reading C Declarations
Introduction SOAC Examples typedef Examples revisited
Introduction
Up until now we have seen straightforward declarations:
void member_display(const struct Library_member *p);void member_display(const struct Library_member *p);
However, they can become much worse:
int *p[15];float (*pfa)[23];long (*f)(char, int);double *(*(*n)(void))[5];
long sum;int* p;
Plus a few trickier ones:
Find the variable being declared Spiral Outwards Anti Clockwise On meeting: say:
* pointer to
[ ] array of
( ) function taking .... and returning
Remember to read “struct S”, “union U” or “enum E” all at once
Remember to read adjacent collections of [ ] [ ] all at once
What is “int * p[15]” ?
int * p [15] ;
p is an array of 15 pointers to integers
What is “double (*p)[38]” ?
double (* p ) [38];
p is a pointer to an array of 38 doubles
What is “short **ab[5][10]” ?
short * * ab [5][10] ;
ab is an array of 5 arrays of 10 arrays of pointers to pointers to short int
What is “long * f(int, float)” ?
long * f (int, float) ;
f is a function taking an int and a float returning a pointer to a long int
What is “int (*pf)(void)” ?
int ( * pf ) (void) ;
pf is a pointer to a function taking no parameters and returning an int
What is “struct Book (*fpa[8])(void)” ?
struct Book ( * fpa[8] ) (void) ;
fpa is an array of 8 pointers to functions, taking no parameters, returning Book structures
What is “char (*(*fprp)(void))[6]” ?
char ( * ( * fprp ) (void) ) [6] ;
fprp is a pointer to a function taking no parameters returning a pointer to an array of 6 char
What is “int * (*(*ptf)(int))(char)” ?
int * ( * ( * ptf ) (int) ) (char) ;
ptf is a pointer to a function, taking an integer, returning a pointer to a function, taking a char, returning a pointer to an int
It doesn’t have to be this difficult! The declaration can be broken into simpler steps
by using typedef To tackle typedef, pretend it isn’t there and read
the declaration as for a variable When finished remember that a type has been
declared, not a variable
Example 1 Revisited
Simplify “int * p[15]”
typedef int * pti ;
pti is a pointer to an int
p is an array of 15 pointer to int
Example 3 Revisited
Simplify “short **ab[5][10]”
typedef short * * pt_pt_s ;
ab is an array of 10 arrays of 5 pointers to pointers to short
typedef pt_pt_s ao5[5];
ao5 ab[10];
ao5 is an array of 5 pointers to pointers to short
pt_pt_s is a pointer to a pointer to a short
Example 5 Revisited
Simplify “int (*pf)(void)”
typedef int fri(void); fri * pf ;
fri is a function, taking no parameters, returning an int
pf is a pointer to a function, taking no parameters,
returning an int
Example 6 Revisited
Simplify “struct Book (*fpa[8])(void)”
typedef struct Book f(void);
f is a function, taking no parameters, returning a
Book structure
typedef f * fp ;
fp is a pointer to a function, taking no parameters,
returning a Book structure
fpa is an array of 8 pointers to functions, taking no parameters, returning a
Example 7 Revisited
Simplify “char (*(*fprp)(void))[6]”
typedef char ( * pta6c ) [6] ;
pta6c is a pointer to an array of 6 char
typedef pta6c f(void);
f is a function, taking no parameters, returning a pointer to an array of 6
fprp is a pointer to a function, taking no
parameters, returning a pointer to an array of 6
Example 8 Revisited
Simplify “int * (*(*ptf)(int))(char)”
typedef pti f(char);
f is a function, taking a char, returning a pointer
typedef f * ptfri ;
ptfri is a pointer to a function, taking a char,
returning a pointer to an int
ptfri ( * ptf )(int) ;
ptf is a pointer to a function, taking int, returning a pointer to a function, taking a
char, returning a pointer to an int
Don’t Panic! SOAC - Spiral Outwards Anti Clockwise To simplify, use typedef(s)
Handling Files in C
Streams stdin, stdout, stderr Opening files When things go wrong - perror Copying files Accessing the command line Dealing with binary files
File handling is not built into the C language itself It is provided by The Standard Library (via a set
of routines invariably beginning with “f”) Covered by The Standard, the routines will
always be there and work the same way, regardless of hardware/operating system
Files are presented as a sequence of characters It is easy to move forwards reading/writing
characters, it is less easy (though far from impossible) to go backwards
Before a file can be read or written, a data structure known as a stream must be associated with it
A stream is usually a pointer to a structure (although it isn’t necessary to know this)
There are three streams opened by every C program, stdin, stdout and stderr
stdin (standard input) is connected to the keyboard and may be read from
stdout (standard output) and stderr (standard error) are connected to the screen and may be written to
What is a Stream?
Although implementations vary, a stream creates a buffer between the program running in memory and the file on the disk
This reduces the program’s need to access slow hardware devices
Characters are silently read a block at a time into the buffer, or written a block at a time to the file
a b c d ef gh i j k l
output stream
a b c de f g hi j
input stream
Why stdout and stderr?
There are two output streams because of redirection, supported by Unix, DOS, OS/2 etc.
printf("written to stdout\n");fprintf(stderr, "written to stderr\n");
C:> outprogwritten to stderrwritten to stdoutC:> outprog > file.txtwritten to stderrC:> type file.txtwritten to stdout
output written to stderr first because it is unbuffered
stdin is Line Buffered
Characters typed at the keyboard are buffered until Enter/Return is pressed
while((ch = getchar()) != EOF)printf("read '%c'\n", ch);
printf("EOF\n");
C:> inprogabcread 'a'read 'b'read 'c'read ''dread 'd'read ''^ZEOFC:>
C:> inprogabcread 'a'read 'b'read 'c'read ''dread 'd'read ''^ZEOFC:>declared as an int, even though
we are dealing with characters
Opening Files
Files are opened and streams created with the fopen function
FILE* fopen(const char* name, const char* mode);FILE* fopen(const char* name, const char* mode);
FILE* in;FILE* out;FILE* append;
in = fopen("autoexec.bat", "r");out = fopen("autoexec.bak", "w");append = fopen("config.sys", "a");
streams, you’ll need one for each
file you want open
if((in = fopen("autoexec.bat", "r")) == NULL) {fprintf(stderr, "open of autoexec.bat failed ");perror("because");return 1;
Dealing with Errors
fopen may fail for one of many reasons, how to tell which?
void perror(const char* message);void perror(const char* message);
open of autoexec.bat failed because: No such file or directoryopen of autoexec.bat failed because: No such file or directory
File Access Problem
Can you see why the following will ALWAYS fail, despite the file existing and being fully accessible?
if((in = fopen("C:\autoexec.bat", "r")) == NULL) {fprintf(stderr, "open of autoexec.bat failed ");perror("because");return 1;
C:> dir C:\autoexec.bat Volume in drive C is MS-DOS_62 Directory of C:\
autoexec bat 805 29/07/90 8:15 1 file(s) 805 bytes 1,264,183,808 bytes freeC:> myprogopen of autoexec.bat failed because: No such file or directory
Displaying a File
char in_name[80];FILE *in_stream;int ch;
printf("Display file: ");scanf("%79s", in_name);
if((in_stream = fopen(in_name, "r")) == NULL) {fprintf(stderr, "open of %s for reading failed ", in_name);perror("because");return 1;
while((ch = fgetc(in_stream)) != EOF)putchar(ch);
fclose(in_stream);
Example - Copying Files#include <stdio.h>
char in_name[80], out_name[80];FILE *in_stream, *out_stream;int ch;
printf("Source file: "); scanf("%79s", in_name);if((in_stream = fopen(in_name, "r")) == NULL) {
fprintf(stderr, "open of %s for reading failed ", in_name);perror("because");return 1;
printf("Destination file: "); scanf("%79s", out_name);if((out_stream = fopen(out_name, "w")) == NULL) {
fprintf(stderr, "open of %s for writing failed ", out_name);perror("because");return 1;
while((ch = fgetc(in_stream)) != EOF)fputc(ch, out_stream);
fclose(in_stream);fclose(out_stream);
Convenience Problem
Although our copy file program works, it is not as convenient as the “real thing”
C:> copyprogSource file: \autoexec.batDestination file: \autoexec.bakC:> dir C:\autoexec.* Volume in drive C is MS-DOS_62 Directory of C:\
autoexec bak 805 31/12/99 12:34autoexec bat 805 29/07/90 8:15 2 file(s) 1610 bytes 1,264,183,003 bytes freeC:> copyprog \autoexec.bat \autoexec.000Source file:
program still prompts despite begin given file names on the command line
Accessing the Command Line
The command line may be accessed via two parameters to main, by convention these are called “argc” and “argv”
The first is a count of the number of words - including the program name itself
The second is an array of pointers to the words
int main(int argc, char *argv[])int main(int argc, char *argv[])
c o p y p r o g . e x e \0
\ a u t o e x e c . b a t \0
\ a u t o e x e c . 0 0 0 \0
int main(int argc, char *argv[]){
for(j = 0; j < argc; j++)printf("argv[%i] = \"%s\"\n", j, argv[j]);
C:> argprog one two threeargv[0] = "C:\cct\course\cprog\files\slideprog\argprog.exe"argv[1] = "one"argv[2] = "two"argv[3] = "three"
Useful Routines
File reading routines:
int fscanf(FILE* stream, const char* format, ...);int fgetc(FILE* stream);char* fgets(char* buffer, int size, FILE* stream);
File writing routines:
int fprintf(FILE* stream, const char* format, ...);int fputc(int ch, FILE* stream);int fputs(const char* buffer, FILE* stream);
long l1, l2;int j, ch;double d;float f;char buf[200];
in = fopen("in.txt", "r") .... out = fopen("out.txt", "w") ....
fscanf(in, "%lf|%li:%li/%i", &d, &l1, &l2, &j);fprintf(out, "%li:%i:%.2lf\n", l1, j, d);
fgets(buf, sizeof(buf), in);fputs(buf, out);
example input
28.325|9000000:68000/1328.325|9000000:68000/13
write that line to the output file (null terminator provided by fgets tells fputs how long the line was)
read next line, or next 199 characters,
whichever is less
ignore next character in input file (newline?)
9000000:13:28.339000000:13:28.33
Binary Files
The Standard Library also allows binary files to be manipulated– “b” must be added into the fopen options
– Character translation is disabled
– Random access becomes easier
– Finding the end of file can become more difficult
– Data is read and written in blocks
size_t fread(void* p, size_t size, size_t n, FILE* stream);size_t fwrite(const void* p, size_t size, size_t n, FILE* stream);
int fseek(FILE* stream, long offset, int whence);long ftell(FILE* stream);void rewind(FILE* stream);
int fgetpos(FILE* stream, fpos_t* pos);int fsetpos(FILE* stream, const fpos_t* pos);
double d;long double lda[35];fpos_t where;
in = fopen("binary.dat", "rb");out = fopen("binnew.dat", "wb");
fread(&d, sizeof(d), 1, in);
fgetpos(in, &where);fread(lda, sizeof(lda), 1, in);
fsetpos(in, &where);fread(lda, sizeof(long double), 35, in);
fwrite(lda, sizeof(long double), 20, out);
fseek(in, 0L, SEEK_END);
read one chunk of 8 bytes
read one chunk of 350 bytes
read 35 chunks of 10 bytes
remember current position in file
return to previous position
write 20 long doubles from ldamove to end of binary.dat
Streams stdin, stdout, stderr fopen opening text files functions: perror, fprintf, fscanf, fgetc, fputc
variables: argc, argv “b” option to fopen to open binary files functions: fread, fwrite, fseek, ftell
Miscellaneous Things
Unions Enumerated types The Preprocessor Working with multiple .c files
A union is a variable which, at different times, may hold objects of different types and sizes
short s;long l;double d;char c;
s.s = 10;s.l = 10L;s.d = 10.01;s.c = '1';
u.s = 10;u.l = 10L;u.d = 10.01;u.c = '1';
Remembering
It is up to the programmer to remember what type a union currently holds
Unions are most often used in structures where a member records the type currently stored
struct preprocessor_const{
char* name;int stored;union{
long lval;double dval;char* sval;
#define N_SIZE 10#define PI 3.1416
struct preprocessor_const s[10000];
s[0].name = "N_SIZE";s[0].u.lval = 10L;s[0].stored = STORED_LONG;
s[1].name = "PI"; s[1].u.dval = 3.1416;s[1].stored = STORED_DOUBLE;
Enumerated Types
Enumerated types provide an automated mechanism for generating named constants
enum day { sun, mon, tue,wed, thu, fri, sat };
enum day today = sun;
if(today == mon)....
#define sun 0#define mon 1#define tue 2#define wed 3#define thu 4#define fri 5#define sat 6
int today = sun;
Using Different Constants
The constants used may be specified
enum day { sun = 5, mon, tue, wed, thu, fri, sat };
enum direction { north = 0, east = 90, south = 180,west = 270 };
What you see is all you get! There are no successor or predecessor functions
The Preprocessor
Preprocessor commands start with ‘#’ which may optionally be surrounded by spaces and tabs
The preprocessor allows us to:
– include files
– define, test and compare constants
– write macros
Including Files
The #include directive causes the preprocessor to “edit in” the entire contents of another file
#define JAN 1#define FEB 2#define MAR 3
#define PI 3.1416
double my_global;
#include "mydefs.h"
double angle = 2 * PI;printf("%s", month[FEB]);
double angle = 2 * 3.1416;printf("%s", month[2]);
Full pathnames may be used, although this is not recommended
#include "C:\cct\course\cprog\misc\slideprog\header.h"#include "C:\cct\course\cprog\misc\slideprog\header.h"
The “I” directive to your local compiler allows code to be moved around much more easily
#include "header.h"#include "header.h"
cc -I c:\cct\course\cprog\misc\slideprog myprog.ccc -I c:\cct\course\cprog\misc\slideprog myprog.c
Constants may be created, tested and removed
#if !defined(SUN)#define SUN 0#endif
#if SUN == MON#undef SUN#endif
if “SUN” is not defined, then begin
define “SUN” as zero
#if SUN > SAT && SUN > MON#if SUN > SAT && SUN > MON
#if WED > 0 || SUN < 3#if WED > 0 || SUN < 3
#if TUE#if TUE if “TUE” is defined with a non zero value
if “WED” is greater than zero or “SUN” is less than 3
if “SUN” is greater than “SAT” and “SUN” is greater than “MON”
if “SUN” and “MON” are equal, then begin
remove definition of “SUN”
Avoid Temptation!
The following attempt to write Pascal at the C compiler will ultimately lead to tears
#define begin {#define end ;}#define if if(#define then )#define integer int
if i > 0 then begini = 17
if( i > 0 ) {i = 17
Preprocessor Macros
The preprocessor supports a macro facility which should be used with care
#define MAX(A,B) A > B ? A : B#define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
int i = 10, j = 12, k;
k = MAX(i, j); printf("k = %i\n", k);k = MAX(j, i) * 2; printf("k = %i\n", k);k = MIN(i, j) * 3; printf("k = %i\n", k);k = MIN(i--, j++); printf("i = %i\n", i);
k = MAX(i, j); printf("k = %i\n", k);k = MAX(j, i) * 2; printf("k = %i\n", k);k = MIN(i, j) * 3; printf("k = %i\n", k);k = MIN(i--, j++); printf("i = %i\n", i); k = 12
k = 12k = 30i = 8
k = 12k = 12k = 30i = 8
A Debugging Aid
Several extra features make the preprocessor an indespensible debugging tool
#define GOT_HERE printf("reached %i in %s\n", \_ _LINE_ _, _ _FILE_ _)
#define SHOW(E, FMT) printf(#E " = " FMT "\n", E)
printf("i = %x\n", i);printf("i = %x\n", i);
printf("reached %i in %s\n", 17, "mysource.c");printf("reached %i in %s\n", 17, "mysource.c");
GOT_HERE;SHOW(i, "%x");SHOW(f/29.5, "%lf");
printf("f/29.5 = %lf\n", f/29.5);printf("f/29.5 = %lf\n", f/29.5);
Working With Large Projects
Large projects may potentially involve many hundreds of source files (modules)
Global variables and functions in one module may be accessed in other modules
Global variables and functions may be specifically hidden inside a module
Maintaining consistency between files can be a problem
Data Sharing Example
extern float step;
void print_table(double, float);
step = 0.15F;
print_table(0.0, 5.5F);
float step;
void print_table(double start, float stop){
printf("Celsius\tFarenheit\n");for(;start < stop; start += step)
printf("%.1lf\t%.1lf\n", start, start * 1.8 + 32);
Data Hiding Example
When static is placed before a global variable, or function, the item is locked into the module
static int entries[S_SIZE];static int current;
void push(int value){
entries[current++] = value}
int pop(void){
return entries[--current];}
static void print(void){}
void push(int value);int pop(void);void print(void);extern int entries[];
push(10); push(15);printf("%i\n", pop());
entries[3] = 77;
double step;
void print_table(double start, double stop){
Use Header Files
Maintain consistency between modules by using header files
NEVER place an extern declaration in a module NEVER place a prototype of a non static (i.e.
sharable) function in a module
Getting it Right
extern double step;
void print_table(double, double);
#include "project.h"
#include <stdio.h>#include "project.h"
Be as Lazy as Possible
Get the preprocessor to declare the variables too!
#if defined(MAIN)#define EXTERN#else#define EXTERN extern#endif
EXTERN double step;EXTERN long current;EXTERN short res;
#define MAIN#include "globals.h"
#include "globals.h"#include "globals.h" #include "globals.h"#include "globals.h"
main.cfirst.c second.c
A union may store values of different types at different times
enum provides an automated way of setting up constants
The preprocessor allows constants and macros to be created
Data and functions may be shared between modules
static stops sharing of data and functions Use the preprocessor in large, multi module
C and the Heap
What is the Heap? Dynamic arrays The calloc/malloc/realloc and free routines Dynamic arrays of arrays Dynamic data structures
What is the Heap?
An executing program is divided into four parts: Stack: provides storage for local variables, alters
size as the program executes Data segment: global variables and strings stored
here. Fixed size. Code segment: functions main, printf, scanf
etc. stored here. Read only. Fixed size Heap: otherwise known as “dynamic memory”
the heap is available for us to use and may alter size as the program executes
How Much Memory?
With simple operating systems like MS-DOS there may only be around 64k available (depending on memory model and extended memory device drivers)
With complex operating systems using virtual memory like Unix, NT, OS/2, etc. it can be much larger, e.g. 2GB
In the future (or now with NT on the DEC Alpha) this will be a very large amount (17 thousand million GB)
Dynamic Arrays
Arrays in C have a fundamental problem - their size must be fixed when the program is written
There is no way to increase (or decrease) the size of an array once the program is compiled
Dynamic arrays are different, their size is fixed at run time and may be changed as often as required
Only a pointer is required
Using Dynamic Arrays
The following steps create a dynamic array: Declare a pointer corresponding to the desired
type of the array elements Initialise the pointer via calloc or malloc using
the total storage required for all the elements of the array
Check the pointer against NULL Increase or decrease the number of elements by
calling the realloc function Release the storage by calling free
calloc/malloc Example
#include <stdio.h>#include <stdlib.h>
unsigned i, s;double *p;
printf("How many doubles? ");scanf("%u", &s);
if((p = calloc(s, sizeof(double))) == NULL) {fprintf(stderr, "Cannot allocate %u bytes "
"for %u doubles\n", s * sizeof(double), s);return 1;
}for(i = 0; i < s; i++)
here we access the “s” doubles from 0..s-1
if((p = malloc(s * sizeof(double))) == NULL) {if((p = malloc(s * sizeof(double))) == NULL) {
all of the allocated memory is freed
realloc Exampledouble *p;double *p2;
printf("%u doubles currently, how many now? ", s);scanf("%u", &s);
p2 = realloc(p, s * sizeof(double));
if(p2 == NULL) {fprintf(stderr, "Could not increase/decrease array "
"to contain %u doubles\n", s);free(p);return 1;
double *p;double *p2;
calculate new array size and allocate
pointer “p” is invalid at this point, so a new value is assigned to it
pointer “p” is still valid at this point
realloc can do it all
The routines malloc and free are almost redundant since realloc can do it all
There is some merit in calloc since the memory it allocates is cleared to zero
p = malloc(s * sizeof(double));p = malloc(s * sizeof(double));
p = realloc(NULL, s * sizeof(double));p = realloc(NULL, s * sizeof(double));
free(p);free(p);
realloc(p, 0);realloc(p, 0);
Allocating Arrays of Arrays
Care must be taken over the type of the pointer used when dealing with arrays of arrays
p = calloc(s, sizeof(float));
float **rain;
rain = calloc(s, 365 * sizeof(float));
float (*rainfall)[365];
rainfall = calloc(s, 365 * sizeof(float));
rainfall[s-1][18] = 4.3F;
Dynamic Data Structures
It is possible to allocate structures in dynamic memory too
struct Node {int data; struct Node *next_in_line;
struct Node* new_node(int value){
struct Node* p;
if((p = malloc(sizeof(struct Node))) == NULL) {fprintf(stderr, "ran out of dynamic memory\n");exit(9);
}p->data = value; p->next_in_line = NULL;
Linking the List
struct Node *first_node, *second_node, *third_node, *current;
first_node = new_node(-100);
second_node = new_node(0);
first_node->next_in_line = second_node;
third_node = new_node(10);
second_node->next_in_line = third_node;
current = first_node;while(current != NULL) {
printf("%i\n", current->data);current = current->next_in_line;
The heap and stack grow towards one another Potentially a large amount of heap storage is
available given the right operating system The routines malloc, calloc, realloc and free
manipulate heap storage Only realloc is really necessary Allocating dynamic arrays Allocating dynamic arrays of arrays Allocating dynamic structures
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C Language. Brief history In 1972, Dennis Ritchie designed C and it was used on PDP-11 mini-computers In 1974, Unix was rewritten in C C++ and C Advantages and disadvantages. A short example. #include <stdio.h> main ( ) { printf (“Is anybody out there?<br>”);
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C Language • Brief history • In 1972, Dennis Ritchie designed C and it was used on PDP-11 mini-computers • In 1974, Unix was rewritten in C • C++ and C • Advantages and disadvantages
A short example • #include <stdio.h> • main ( ) • { • printf (“Is anybody out there?\n”); • printf (“Hello world!\n”); • }
/* Another example-read items, compute their average */ • #include <stdio.h> • main ( ) • { • int ItemsRead = 0; • double ThisItem, Sum = 0.0; • printf (“Enter as many items as you want\n”); • printf (“Terminate with non-double or EOF marker\n”); • while (scanf (“%lf”, &ThisItem ) ==1 ) • { • ItemsRead ++; • Sum += ThisItem; • } • printf( “The average of %d items was %f\n”, ItemsRead, Sum / ItemsRead ); • return 0; • }
Simple C • 1. Create a c program • Any line or screen editor will do. Vi editor is also a good choice. For simple ones, one can use cat > fileName as well. • 2. Compile the program • cc fileName.c will create a executable file called a.out regardless of the fileName.
Compile with a style • To create a complied file with the same name: • Use ccfileName.c –o fileName • Will create a file with the fileName instead of a.out
Compiling Problems • It is not as straightforward as the Code Warrior you did in C++ course. • However, you will get used to it once you do more. • Unix debugger dbx is available for debugging.
Memory leak in C • Memory leaks (in which malloc() memory is never released with corresponding free() calls) and buffer overruns (writing past memory that has been allocated for an array, for example) are some of the common problems and can be difficult to detect.
Example • #include <stdlib.h> • #include <stdio.h> • #include "memwatch.h" • int main(void) • { • char *ptr1; • char *ptr2; • ptr1 = malloc(512); • ptr2 = malloc(512); • ptr2 = ptr1; • free(ptr2); free(ptr1); • }
What is the problem with that program? • The code in Listing 1 allocates two 512-byte blocks of memory, and then the pointer to the first block is set to the second block. As a result, the address of the second block is lost, and there is a memory leak.
Debug Tools • There are various ways to track down user-space and kernel problems using debug tools on Linux. Build and debug your source code with these tools and techniques: • Memory tools: MEMWATCH and YAMD • strace • GNU debugger (gdb) • Magic key sequence
Compiling Process • 1. cc command translate the source file to an equivalent assembly program. • 2. Once an equivalent assembly language is generated, another program called assembler is called to convert the program into binary file or machine code file. • 3. Finally, linker is called to combine the binary file with the library to create a executable file.
cc versus gcc • gcc – the GNU C Compiler, it was written by Richard Stallman and it is now maintained by Cyguns solutions. gcc exists for practically all major operating systems and processor architectures and is widely used in embedded systems. • 1. It is the complier we are using in Linux. • 2. When you invoke cc, you are invoking gcc
gcc interpretation of filename Suffixes • .c --- C source code which must be pre- • processed before compilation. • .i --- C source code has been pre-processed. • .cc, .cxx, .cpp, .C --- C++ source file as in .c • .ii --- C++ source that has been pre-proce… • .h --- C header file • .s --- Assembly code • .S --- Assembly code which must be pre-processed
Compiling C++ Programs • To compile and link C++ programs, you should invoke the complier as g++ rather than gcc. This is especially important at link time because it force the linker to link in certain libraries required by C++ programs.
Basic Rules in C • The basic unit of a C program is a character. • A-Z, a-z, 0-9, white space: blanks, newlines, tabs, … and the following 29 characters: • ! # % ^ & * ( ) _ - + = [ ] { } | \ ; : “ ‘ < > • , . / ? ~ • White space is important for readability.
Comments in C • 1. C comments begins with a /* and end with */ and there should be no space between the asterisk and the slash. • 2. No nest in comment in C. • Common error: • /* 1 */ /* This comment ends early on the next line. • /* 2 */ * This is not in the comment ! • /* 3 */ * Nether is this;
Identifiers and Keywords in C • 1. A name may use A-Z, a-z, 0-9, _ • Begin with a digit is prohibited. • 2. The length cannot exceed 31 chars and in • some situations 6 is the limit. • 3. Similar to the UNIX, c is case sensitive. • 4. Avoid using the 32 keywords. • They are:
Keywords in C • auto, break, case, char, const, continue, • default, do, double, else, enum, extern • float, for, goto, if, int, long, register, return • short, signed, sizeof, static, struct, switch • typedef, union, unsigned, void, volatile, • while
Pre-Processor in C • #include <stdio.h> • #define Minimum Wage 5.75 • #---the first non-white-space character line begins with # will be treated as pre-processor • < ***> inside indicates the *** file doe not reside in the current directory, (it resides in the system directory) • .h --- h refer to the header file similar to C++
Pointers in C • Pointer is a variable to store an address of another object. • That object is accessed by dereferencing the • Pointer. • Pointer is one of the most important concept in C language
How to define a pointer? • int *p; • int x = 8; • int *p = &x; /* p points at x */ • ++*p will change x to 9 while • *P++ will make the pointer points to a different number in memory.
Pointer in C • You can give a pointer any name you like, such as: • int *p, int *ptr, int *Ptr, int *xPointer • However, we recommend use *xptr or xPtr to point x and *yPtr to point y. • * --- is called indirection operator or dereferencing operator.
Initializing Pointer • Pointer should be initialized either when they are declared or in an assignment statement. • int *xPtr, *yPtr, *zeroPtr; • int x = 8, y = 9, zero = 0; • xPtr = &x; • yPtr = & y; • zeroPtr = NULL or zeroPtr = 0; • NULL is a symbolic constant defined in the <stdio.h> header file (and in several other header files)
What we care is p points to the variable by store the address in it. The computer will reserve a address for p. However, we don’t care where it will store it. address p 8 p ++*p will make 8 becomes 9 and *p++ will make p points to another address
Program Example • #include <stdio.h> • Void • Swap (int * const X, int * const Y) • { • int Temp; • Temp = *X; • *X = *Y; • *Y = Temp; • } • main (void) • { • int A = 5, B = 7; • Swap (&A, &B); • printf (“%/d %/d\n” , A, B); /* Must pass the address */ • return 0; • }
Input from c Programs scanf • #include <stdio> • main (void) • { • int x; • double y; • printf (“Enter an integer and a real: “); • scanf ( “%d %lf” , &x , &y); • Print (“You entered %d and %f\n” , x, y); • }
Example • #include <stdio.h> • int main ( ) { printf(“\”So what? \“ said she.\n”); return 0; }
Input in c • #include <stdio.h> • int main( void ) • { • int intvar; • printf("The address of intvar is %p.\n", &intvar); printf("\nEnter an integer value: "); • scanf("%d", &intvar); printf("The value you entered was %d.\n", intvar); • return 0; • }
Notice the problem when you run the program • 1. When you input a legal integer. • 2. When you input a serious of characters. • 3. When you input a number that is too big to the computer.
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C language ppt. 1. Presented By : Gaurav Juneja. 2. Introduction C is a general purpose language which is very closely associated with UNIX for which it was developed in Bell Laboratories. Most of the programs of UNIX are written and run with the help of 'C'. Many of the important ideas of 'c' stem are from BCPL by Martin Richards. In 1972 ...
Mar 2, 2021 • 2 likes • 993 views Arunima Education Foundation Follow The presentation on C programming languages illustrates and explains the concept of Computer programming language. The base language used is C programming with its features, advantages, disadvantages and characteristics of a good program.
Cp Sc 1110 - Programming in C 4th Edition Slides and Handouts: Chapter: Slides: Handouts: 01 Introduction to C: Slides: Handouts: 02 Your First Program
Home > PowerPoint Slides > Introduction To C Programming Published in: C, C++ 25,579 Views what is C? How it is useful and how to write a simple C program and the C mechanism. Devi / Chennai 6 years of teaching experience Qualification: B.Tech/B.E. ( Saveetha Engineering College, Chennai - 2017)
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Introduction to C language powerpoint presentation @Computing Coder 0:00 Intro0:13 what is a program0:21 what is algorithm0:27 what is flowchart0:41 what ...
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Special Symbols Operators Character & String. 3 1. Keywords Keywords are the reserved words whose meaning has already been explained to the C compiler. C has 32 keywords. These keywords combined with a formal syntax form a C programming language. Rules to be followed for all programs written in C: All keywords are lower-cased.
Introduction to C language powerpoint presentation @Computing Coder 0:00 Intro0:11 Data types in C0:55 Operators in C1:20 Hierarchy of Operators 1:28 Ass...
Module 1 Introduction Introduction to components of a Computer System Introduction to Algorithm and Flowchart Fundamentals of C Programming Keywords, Identifiers, Constants and Variables Data types in C Operators in C Basic Input and Output Operations Expressions and Precedence of Operators In-built Functions Module 2 Control Structures
Introduction To C Programming Language Presentation Slide C is a high-level programming language that was originally developed in the early 1970s for system programming and has since become widely used for a variety of applications.
rules for C / C++ variable names are followed and must be unique. 2. Parameter list - Many functions use arguments, the value passed to the function when it is called. A function needs to know the data type of each argument. Argument type is provided in the function header by the parameter list. Parameter list acts as a placeholder. www.tenouk ...
Features of C. C can be thought of as a "high level assembler" Designed for maximum processor speed Safety a definite second! THE system programming language (Reasonably) portable Has a "write only" reputation
Jul 2, 2010 • 1,038 likes • 211,305 views Abhishek Dwivedi Follow This C tutorial covers every topic in C with the programming exercises. This is the most extensive tutorial on C you will get your hands on. I hope you will love the presentation. All the best. Happy learning. Feedbacks are most welcome. Send your feedbacks to [email protected].
C Features • Middle-level language • Can access bit level • Machine independent • Case sensitive • Type language (weak type) • Variable must be declared a type • Allow automatic type conversion • No boolean data type (0: false, non-zero: true) • No run-time error checking • Programmer's responsibility: array boundary
PPT - C Language PowerPoint Presentation, free download - ID:2185379 Presentation Download 1 / 16 Download Presentation >> C Language Jul 22, 2014 170 likes | 495 Views C Language. 219212 Programming Languages Ms. Raviporn Yongchaitrakul ID: 47541396. ABSTRACT.
PPT - C programming language PowerPoint Presentation, free download - ID:4189213 1 / 18 Download Presentation >> C programming language Sep 10, 2014 1.47k likes | 2.68k Views C programming language. Md. Hafizur Rahman, MSc in DUET. Introduction.
2. Intro C is the famous programming language designed to develop system application program. 3. Intro It is known as the starting of every programming language all the basics of a program language starts from C language. C is known as general purpose procedural programming language. 4.
The C programming language (While loop) C, C++. 86 Views. The C Programming Language - Chapter 4 (part 1) C, C++. 77 Views. Introduction To Programming Languages ... 16,992 Views. Upload PPTs . If you have your own PowerPoint Presentations which you think can benefit others, please upload on LearnPick. For each approved PPT you will get 50 ...
Simple C • 1. Create a c program • Any line or screen editor will do. Vi editor is also a good choice. For simple ones, one can use cat > fileName as well. • 2. Compile the program • cc fileName.c will create a executable file called a.out regardless of the fileName.
Structure initialization • Syntax: struct structure_name structure_variable= {value1, value2, … , valueN}; • There is a one-to-one correspondence between the members and their initializing values. • Note: C does not allow the initialization of individual structure members within the structure definition template. 8.
POINTERS IN C Home > PowerPoint Slides > POINTERS IN C Published in: C, C++ 28,374 Views This PPT includes Introduction to pointers, Pointer using Arrays, Function Pointer, Pointers to Structures.. Praveen R / Chennai 5 years of teaching experience Qualification: MCA