Infinite Loop in C

An infinite loop is a loop that does not naturally stop because its condition remains true. It can be intentional, such as a server/menu loop, but an accidental infinite loop is usually a bug.

Syntax / Basic Pattern

while (1) {
/* stop using break when required */
}

Easy points to remember

Use a clear exit condition when possible.
break can be used to stop an intentional infinite loop.
Always test infinite loops carefully so the program can exit.

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

Program 1: while(1) with break

#include <stdio.h>
int main(){int i=1;while(1){printf(“%d “,i);if(i==3)break;i++;}return 0;}

OUTPUT
1 2 3

Program 2: for(;;) with break

#include <stdio.h>
int main(){int i=1;for(;;){printf(“%d “,i);if(i==4)break;i++;}return 0;}

OUTPUT
1 2 3 4

Program 3: Menu-style loop

#include <stdio.h>
int main(){int choice=2;while(1){printf(“Choice=%d”,choice);if(choice==2)break;}return 0;}

OUTPUT
Choice=2

Program 4: Countdown

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

OUTPUT
5 4 3 2 1

Program 5: Find first multiple

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

OUTPUT
7

Program 6: Find square

#include <stdio.h>
int main(){int i=1;while(1){if(i*i>=30){printf(“%d”,i*i);break;}i++;}return 0;}

OUTPUT
36

Program 7: Sum until 5

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

OUTPUT
15

Program 8: Print even then stop

#include <stdio.h>
int main(){int i=2;while(1){printf(“%d “,i);if(i==8)break;i+=2;}return 0;}

OUTPUT
2 4 6 8

Program 9: Power until >=100

#include <stdio.h>
int main(){int p=1;while(1){p*=2;if(p>=100)break;}printf(“%d”,p);return 0;}

OUTPUT
128

Program 10: Search digit

#include <stdio.h>
int main(){int n=4826,d;while(1){d=n%10;if(d==8){printf(“Found 8”);break;}n/=10;if(n==0){printf(“Not found”);break;}}return 0;}

OUTPUT
Found 8

Program 11: Stop at 0

#include <stdio.h>
int main(){int a[]={4,3,0,9},i=0;while(1){if(a[i]==0)break;printf(“%d “,a[i]);i++;}return 0;}

OUTPUT
4 3

Program 12: Prime-like test

#include <stdio.h>
int main(){int n=29,i=2,prime=1;while(1){if(i*i>n)break;if(n%i==0){prime=0;break;}i++;}printf(“%s”,prime?”Prime”:”Not prime”);return 0;}

OUTPUT
Prime

Program 13: Fibonacci stop

#include <stdio.h>
int main(){int a=0,b=1,c;while(1){printf(“%d “,a);if(a>=10)break;c=a+b;a=b;b=c;}return 0;}

OUTPUT
0 1 1 2 3 5 8 13

Program 14: Attempts

#include <stdio.h>
int main(){int attempts=0;while(1){attempts++;if(attempts==3)break;}printf(“Attempts=%d”,attempts);return 0;}

OUTPUT
Attempts=3

Program 15: Infinite loop concept

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

OUTPUT
Run1 Run2