Question

Foundation of Computer Science

Discuss the repetition constructs. Give an illustrative example for each one of them.

Answer 1

Repetition constructs , or loops, are used when a program needs to repeatedly
process one or more instructions until some condition is met, at which time the
loop ends. The process of performing the same task over and over
again is called iteration.
A loop executes the same part of program code over and over again, as long as
a loop condition with each repetition. This section of code
can be a single statement or a block of statements (a compound statement).

There are three types of repetition constructs:
1. for loop
2. while loop
3. do ... while loop

Syntax of for loop:

for(expression 1; condition; expression 2){
--body of the loop--
}
Steps of execution:
Step 1: The control first goes to expression 1.
Step 2: Then it goes to condition. If it is true,
then it enters body of the loop and executes it. After that, it goes to expression 2.
Then again to Step 2. If the condition is false, then loop breaks and control comes out of the loop

Example of for loop:
To print Natural Numbers from 1 to 10:

for(int i=1;i<=10;i++){
printf("%d ",i);
}

// Output:

1 2 3 4 5 6 7 8 9 10

Syntax of while loop:

while(condition){
--body of loop--
}
Steps of execution:
Step 1: The control first goes to condition.If it is true, then it goes to body. If it is false, then it comes out of loop.
Step 2: Control goes to the body of the loop, executes it and goes back to Step 1.

Example of while loop:
To print Natural Numbers from 1 to 10:

int i = 1;
while(i<=10){
printf("%d ",i);
i++;
}

// Output:

1 2 3 4 5 6 7 8 9 10

Syntax of do while loop:

do{
--body of loop--
}
while(condition);

Steps of execution:
Step 1: The statement executes first, and then expression is evaluated
Step 2: If expression evaluates to true, statement executes again
Step 3: As long as expression in a do...while statement is true, statement executes
Step 4: Like other loops, to avoid an infinite loop, loop body must contain a statement that makes expression false
Step 5: Statement can be simple or compound (multiple statements); if compound, they must be in braces

Example of do ... while loop:
To print Natural Numbers from 1 to 10:

int i = 1;
do{
printf("%d ",i);
i++;
}
while(i<=10);

// Output:

1 2 3 4 5 6 7 8 9 10