Technically its very important to know when to use for, while and repeat-until loop while we are coding based on the requirement. Since all the 3 loops are used to perform incremental task. Developers must be properly knowing when to use For loop, while loop and repeat-until loop.
So, the major reason between these three loops is:
1. For loop:
For loop is used if we know the number of times the statement needs to be executed.
FOR var := 1 TO 5 DO
BEGIN
//statement
END;
output:
//statement
//statement
//statement
//statement
//statement
In this case the statement is executed 5 times.
2. While loop:
While loop will not execute if the condition is false.
var := 0;
WHILE var <> 0 DO BEGIN
var := var - 1;
//statement
END;
output:
In this case the condition is failed. So while loop never gets executed.
3. Repeat-Until loop:
var := 0;
REPEAT
var := var - 1;
//statement
UNTIL var <> 0;
Output:
//statement
In this case as you see whether the condition is true/false but the statement is executed at least once.
So, the major reason between these three loops is:
1. For loop:
For loop is used if we know the number of times the statement needs to be executed.
FOR var := 1 TO 5 DO
BEGIN
//statement
END;
output:
//statement
//statement
//statement
//statement
//statement
In this case the statement is executed 5 times.
2. While loop:
While loop will not execute if the condition is false.
var := 0;
WHILE var <> 0 DO BEGIN
var := var - 1;
//statement
END;
output:
In this case the condition is failed. So while loop never gets executed.
3. Repeat-Until loop:
var := 0;
REPEAT
var := var - 1;
//statement
UNTIL var <> 0;
Output:
//statement
In this case as you see whether the condition is true/false but the statement is executed at least once.