For in Ada

Different Types of for Loops in Ada#

Ada’s looping constructs offer a versatile range of loop types similar in functionality. Here’s how you can achieve different types of looping constructs in Ada.

Basic Loop with a Single Condition#

The most basic loop type uses a condition to control the repetition.

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
    declare
        I : Integer := 1;
    begin
        while I <= 3 loop
            Put_Line(Integer'Image(I));
            I := I + 1;
        end loop;
    end;
end Main;

Classic Initial/Condition/Iteration Loop#

This type of loop explicitly initializes the loop variable, checks the condition, and updates the variable after each iteration.

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
    for J in 0 .. 2 loop
        Put_Line(Integer'Image(J));
    end loop;
end Main;

Iteration Using for Loop Range#

Ada’s for loop can also iterate over a range with ease which is similar to iteration using range.

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
    for I in 0 .. 2 loop
        Put_Line("range" & Integer'Image(I));
    end loop;
end Main;

Infinite Loop with break Equivalent#

A loop without a condition will repeat indefinitely until it encounters an exit statement to break out of the loop (equivalent to break).

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
    loop
        Put_Line("loop");
        exit;
    end loop;
end Main;

Using continue Equivalent in a Loop#

In Ada, the concept of continue is achieved using exit when followed by the condition you’d like to skip.

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
    for N in 0 .. 5 loop
        if N mod 2 = 0 then
            -- Continue to the next iteration
            null;
        else
            Put_Line(Integer'Image(N));
        end if;
    end loop;
end Main;

Running the Ada Program#

To run an Ada program, you need to compile the .adb file yielding an executable which can then be run.

$ gnatmake main.adb
$ ./main

Expected output for running the compiled program:

1
2
3
0
1
2
range 0
range 1
range 2
loop
1
3
5

Gaining familiarity with these looping constructs will help in writing efficient Ada programs. In future examples, we’ll explore more detailed structures and functionalities in the language.