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Prime number tester

#include <stdio.h> int main(void) { int num, j, is_prime; printf("Enter a number: "); scanf("%d", &num); is_prime = 1; for(j = 2; j <= num / 2; j = j + 1) if((num%j)==0) is_prime = 0; if(is_prime==1) printf(" is prime."); else printf("not prime."); return 0; }