Thread: Why am I getting an infinite loop?

Its a program to print the prime factors of a positive integer.
For e.g. the prime factors of 2520 are 2,2,2,3,3,5,7 and 1.

Code:

#include<stdio.h>
int prime(int x);
int main(void)
{
     int a;
     printf("Enter a positive integer");
     scanf("%d",a);
     prime(a);
}
int prime(int x)
{
     while(x%2==0)
     {
       printf("2");
       x=x/2;
     }
     while(x%3==0)
     {
       printf("3");
       x=x/3;
     }
     while(x%5==0)
     {
       printf("5");
       x=x/5;
     }
     while(x%7==0)
     {
       printf("7");
       x=x/7;
     }
     while(x%9==0)
     {
       printf("9");
       x=x/9;
     }
     while(x%11==0)
     {
       printf("11");
       x=x/11;
     }
     printf("x");
}

The logic seems to be right,
For e.g. say if the integer is 1232 then it passes the first while loop and prints 2 four times until the value of x becomes 77 then it passes the while loop of 3 but as x%3 is not 0,it leaves the while loop of 3 and enters the while loop of 5,as x%5 is not 0,it leaves the loop and enters the while loop of 7 and prints 7 one time then the value of x becomes 11 and the control enters the while loop of 11 and 11 is printed one time then x becomes 1 and 1 is printed one time.So I should get the output as 2,2,2,2,7,11,1 but I am getting an infinite loop of 2?

Code:

scanf("%d",&a);

You may want to start with these errors/warnings:

main.c||In function ‘main’:|
main.c|7|warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat]|
main.c||In function ‘prime’:|
main.c|43|warning: control reaches end of non-void function [-Wreturn-type]|
main.c||In function ‘main’:|
main.c|7|warning: ‘a’ is used uninitialized in this function [-Wuninitialized]|
||=== Build finished: 0 errors, 3 warnings ===|

Jim

lol i liked this program, so i modded it!!!
added the first 120 primes to an array

next i might just have the program make the primes to check against! ok yeah i will!

Code:

//Crossfire Softwarez//

#include<stdio.h>
void prime(int x);
int main(void)
{     
 int a;     
 printf("Enter a positive integer: ");     
 scanf("%d",&a);     
 prime(a);
 return 0;
}
void prime(int x)
{     
 
 int Primes[120]={2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,
     73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 
     179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281,
     283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409,
     419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541,
     547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659};
 
 for(int counter = 0; counter <=120;counter++)
  {
   while(x%Primes[counter]==0)     
    {       
     printf("%i ",Primes[counter]);       
     x=x/Primes[counter];     
    }
  }     
 
 printf("\n");
 
}

Originally Posted by laserlight

This is a mistake: counter <=120

yeah cought that, i went 1 too many!!!

i like this better!!!

Code:

//Crossfire Softwarez// 
#include<stdio.h>

int main(void)
{
 int found;    
 int num;
    printf("Enter a positive integer: ");
    scanf("%d",&num);
 
 for(int factor = 2; factor <= 10000;factor++)
  {
   found = 0;
   for(int counter = 2; counter <= factor;counter++)
    {
     if(factor%counter==0)
      {
       found++;
      }
    }
   if (found < 2)
    {
     while(num%factor==0)         
      {            
       printf("%i ",factor);
                num=num/factor;
             }
    }
 
  }
 printf("\nall factors found\n");
 return 0;
}

i think i am having more fun with other peoples codes then my own!!! :P