ada string assignment

Advanced Techniques

Ada supports scope-based resources, also called RAII by extending the Controlled or LimitedControlled types.

Timing out on a Blocking Operation ​

Waiting for all tasks to complete ​.

A list of statements doesn't exit until all tasks are complete, so by using declare ... begin ... end you can wait until all your tasks are done.

• Timing out on a Blocking Operation
• Waiting for all tasks to complete

Ada Programming/Variables

• 1 Assignment statements
• 3.1 Ada Reference Manual

Variables are references that stand in for a value that is contained at a certain memory address.

Variables are said to have a value and may have a data type . If a variable has a type, then only values of this type may be assigned to it. Variables do not always have a type.

A value can have many values of many different types: integers (7), ratios (1/2), (approximations of) reals (10.234), complex numbers (4+2i), characters ('a'), strings ("hello"), and much more.

Different languages use different names for their types and may not include any of the above.

Assignment statements [ edit source ]

An assignment statement is used to set a variable to a new value.

Assignment statements are written as name := value .

The example set the variable X to the integer value of 10 . The assignment statement overwrites the contents of the variable and the previous value is lost.

In some languages, before a variable can be used, it will have to be declared, where the declaration specifies the type.

Ada is the same. The declaration is as follows:

Uses [ edit source ]

Variables store everything in your program. The purpose of any useful program is to modify variables.

See also [ edit | edit source ]

Ada reference manual [ edit | edit source ].

• 3.3 Objects and Named Numbers ( Annotated )

• Book:Ada Programming
• Book:Ada Programming/Pages containing deprecated templates

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8.4.7 String Handling guideline Use the predefined packages for string handling. example Writing code such as the following is no longer necessary in Ada 95: function Upper_Case (S : String) return String is subtype Lower_Case_Range is Character range 'a'..'z'; Temp : String := S; Offset : constant := Character'Pos('A') - Character'Pos('a'); begin for Index in Temp'Range loop if Temp(Index) in Lower_Case_Range then Temp(Index) := Character'Val (Character'Pos(Temp(Index)) + Offset); end if; end loop; return Temp; end Upper_Case; with Ada.Characters.Latin_1; function Trim (S : String) return String is Left_Index : Positive := S'First; Right_Index : Positive := S'Last; Space : constant Character := Ada.Characters.Latin_1.Space; begin while (Left_Index < S'Last) and then (S(Left_Index) = Space) loop Left_Index := Positive'Succ(Left_Index); end loop; while (Right_Index > S'First) and then (S(Right_Index) = Space) loop Right_Index := Positive'Pred(Right_Index); end loop; return S(Left_Index..Right_Index); end Trim; Assuming a variable S of type String , the following expression: Upper_Case(Trim(S)) can now be replaced by more portable and preexisting language-defined operations such as: with Ada.Characters.Handling; use Ada.Characters.Handling; with Ada.Strings; use Ada.Strings; with Ada.Strings.Fixed; use Ada.Strings.Fixed; ... To_Upper (Trim (Source => S, Side => Both)) rationale The predefined Ada language environment includes string handling packages to encourage portability. They support different categories of strings: fixed length, bounded length, and unbounded length. They also support subprograms for string construction, concatenation, copying, selection, ordering, searching, pattern matching, and string transformation. You no longer need to define your own string handling packages.

• Introduction to Ada

So far, all the types we have encountered have values that are not decomposable: each instance represents a single piece of data. Now we are going to see our first class of composite types: records.

Records allow composing a value out of instances of other types. Each of those instances will be given a name. The pair consisting of a name and an instance of a specific type is called a field, or a component.

Record type declaration 

Here is an example of a simple record declaration:

Fields look a lot like variable declarations, except that they are inside of a record definition. And as with variable declarations, you can specify additional constraints when supplying the subtype of the field.

Record components can have default values. When a variable having the record type is declared, a field with a default initialization will be automatically set to this value. The value can be any expression of the component type, and may be run-time computable.

In the remaining sections of this chapter, we see how to use record types. In addition to that, we discuss more about records in another chapter .

Aggregates 

Records have a convenient notation for expressing values, illustrated above. This notation is called aggregate notation, and the literals are called aggregates. They can be used in a variety of contexts that we will see throughout the course, one of which is to initialize records.

An aggregate is a list of values separated by commas and enclosed in parentheses. It is allowed in any context where a value of the record is expected.

Values for the components can be specified positionally, as in Ada_Birthday example, or by name, as in Leap_Day_2020 . A mixture of positional and named values is permitted, but you cannot use a positional notation after a named one.

Component selection 

To access components of a record instance, you use an operation that is called component selection. This is achieved by using the dot notation. For example, if we declare a variable Some_Day of the Date record type mentioned above, we can access the Year component by writing Some_Day . Year .

Let's look at an example:

As you can see in this example, we can use the dot notation in the expression D . Year or Some_Day . Year to access the information stored in that component, as well as to modify this information in assignments. To be more specific, when we use D . Year in the call to Put_Line , we're retrieving the information stored in that component. When we write Some_Day . Year := 2001 , we're overwriting the information that was previously stored in the Year component of Some_Day .

In previous chapters, we've discussed subprogram and package renaming. We can rename record components as well. Instead of writing the full component selection using the dot notation, we can declare an alias that allows us to access the same component. This is useful to simplify the implementation of a subprogram, for example.

We can rename record components by using the renames keyword in a variable declaration. For example:

Here, Y is an alias, so that every time we using Y , we are really using the Year component of Some_Day .

Let's look at a complete example:

We apply renaming to two components of the Date record in the implementation of the Increase_Month procedure. Then, instead of directly using Some_Day . Month and Some_Day . Year in the next operations, we simply use the renamed versions M and Y .

Note that, in the example above, we also rename Months ' Succ — which is the function that gives us the next month — to Next .

How do you display just string on this label, and to make it show multiple entries in order (not just last entered)

I would like to store string on page one then recall in order showing just data on page two. thanks

in screen1, you saved data to 2 fixed tag, that means you can only save 2 data set, every time you save, the new data will overwrite the old one. to fix this, you can use the date as tag, the notes as value to store.

in screen2, in the for loop, you need to set label.text to JOIN (label.text, '\n', tinydb.getValue(item,''))

Thanks Kevin, how would that look? how do I display more than one result without the {''date'',''details''} showing?

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