terminate - My C code doesn't output anything, or end running -
    i'm trying answer question:   the prime factors of 13195 5, 7, 13 , 29.   what largest prime factor of number 600851475143 ?   here code:   #include <stdio.h>  int isprime(long long num) {     (long long k = 1; k < num; k++)     {             if (num%k == 0)                     return 0;     }      return 1; }  long long num = 600851475143; int main(void) {     long long prime_factor = 0;     (long long j = 2; j < num; j++)     {             if (num % j == 0 && isprime(j) == 1)                     prime_factor = j;     }      printf("%lli\n", prime_factor);   }   but reason doesn't print anything, or end.  causing this?          that's terribly inefficient way of finding prime factors of number.   to find prime factors, should:         create static list of primes less or equal (number / 2).    iterate on each element in list of primes , see if each    1 can evenly divide number.    divide original number prime, , check last number    again...