C - Loops

While writing a program, there may be a situation when you need to repeat a block of code again and again up to certain number of times or up to infinity. In such situation, you would need to write loop statements. Loop is also known as iteration.

Advantages of Loops

1. Reduce redundancy of code.
2. Makes program less complex.
3. It helps to traverse the elements of array.

In C-Language, there are 3 types of loops available:

for loop
while loop
do...while loop

For loop iterates the code until the condition is false. For loop uses initialization, and increment/decrement at the time of checking the condition.

• Initialization is the initial value from where the loop starts execution.
• Condition will execute a loop until condition is false.
• Increment/decrement will change the variable value for the next iteration.

Example 1: WAP to print counting 1 to 10 using For Loop. 1

#include<stdio.h>
int main()
{
    int i;
    //for(initialization; condition; inc/dec)
    for(i=1; i<=10; i++)
    {
        printf("For Loop %d ",i);
    }
    return 0;
}

For loop is useful when the number of iteration is known to the user.

In While loop, initialization statement appears before the while loop begins, condition appears to test the loop, increment/decrement statement will appear inside the while loop to change the variable value for the next iteration. It is better if number of iterations is not known by the user.

Example 2: WAP to print counting 1 to 10 using While Loop. 1

#include<stdio.h>
int main()
{
    int i=1; //initialization
    while(i<=10) //condition 
    {
        printf("While Loop %d ",i);
        i++; //increment
    }
    return 0;
}

While loop is use where number of iteration is not known by the user.

Do while loop is similar to while loop, only the different is that the condition appears in the end. So, the code is executed at least once, even if the condition is false in the beginning.

Example 3: WAP to print counting 1 to 10 using Do While Loop. 1

#include<stdio.h>
int main()
{
    int i=1; //initialization
    do {
        printf("Do while loop %d ",i);
        i++; //increment
    }while(i<=10); //condition
    return 0;
}

Do while loop is used where you want to execute the code at least once.

Example 4: WAP to explain the use of While Loop. 1

#include<stdio.h>
int main()
{
    int n=1; //initialization
    while(n!=0)
    {
        printf("\nEnter Number (0-exit)");
        scanf("%d",&n);
    }
    return 0;
}

If you pass 1 as an expression or any value other than 0, then the condition is true, 0 means false.

Example 5: Infinitive while loop.

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

Example 6: Infinitive do while loop

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

Example 7: Infinitive for loop

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