While loop in C

A while loop checks its condition before each repetition. If the condition is false at the beginning, the body may execute zero times.

Syntax / Basic Pattern

while (condition) {
// body
}

Easy points to remember

Initialize the control variable before the loop.
Change the control variable inside the loop when required.
Use while when the number of repetitions is not necessarily known in advance.

⭐ PRACTICE TIP: Type these programs yourself. Change the values and run them again. That is how control statements become easy.

Program 1: Print 1 to 5

#include <stdio.h>
int main(){int i=1;while(i<=5){printf(“%d “,i);i++;}return 0;}

OUTPUT
1 2 3 4 5

Program 2: Print 5 to 1

#include <stdio.h>
int main(){int i=5;while(i>=1){printf(“%d “,i);i–;}return 0;}

OUTPUT
5 4 3 2 1

Program 3: Sum 1 to 10

#include <stdio.h>
int main(){int i=1,s=0;while(i<=10){s+=i;i++;}printf(“%d”,s);return 0;}

OUTPUT
55

Program 4: Even numbers

#include <stdio.h>
int main(){int i=2;while(i<=10){printf(“%d “,i);i+=2;}return 0;}

OUTPUT
2 4 6 8 10

Program 5: Odd numbers

#include <stdio.h>
int main(){int i=1;while(i<=9){printf(“%d “,i);i+=2;}return 0;}

OUTPUT
1 3 5 7 9

Program 6: Table

#include <stdio.h>
int main(){int i=1;while(i<=10){printf(“%d “,7*i);i++;}return 0;}

OUTPUT
7 14 21 28 35 42 49 56 63 70

Program 7: Factorial

#include <stdio.h>
int main(){int i=1,f=1;while(i<=5){f*=i;i++;}printf(“%d”,f);return 0;}

OUTPUT
120

Program 8: Count digits

#include <stdio.h>
int main(){int n=7603,c=0;while(n){c++;n/=10;}printf(“%d”,c);return 0;}

OUTPUT
4

Program 9: Reverse

#include <stdio.h>
int main(){int n=456,r=0;while(n){r=r*10+n%10;n/=10;}printf(“%d”,r);return 0;}

OUTPUT
654

Program 10: Sum digits

#include <stdio.h>
int main(){int n=739,s=0;while(n){s+=n%10;n/=10;}printf(“%d”,s);return 0;}

OUTPUT
19

Program 11: Power

#include <stdio.h>
int main(){int i=1,p=1;while(i<=4){p*=2;i++;}printf(“%d”,p);return 0;}

OUTPUT
16

Program 12: Squares

#include <stdio.h>
int main(){int i=1;while(i<=5){printf(“%d “,i*i);i++;}return 0;}

OUTPUT
1 4 9 16 25

Program 13: Multiples of 6

#include <stdio.h>
int main(){int i=6;while(i<=30){printf(“%d “,i);i+=6;}return 0;}

OUTPUT
6 12 18 24 30

Program 14: Count down by 2

#include <stdio.h>
int main(){int i=10;while(i>=2){printf(“%d “,i);i-=2;}return 0;}

OUTPUT
10 8 6 4 2

Program 15: Find first multiple

#include <stdio.h>
int main(){int i=1;while(i%9!=0)i++;printf(“%d”,i);return 0;}

OUTPUT
9