1 #include 
     
       2  3 bool If_prime(int a,int b) 4 { 5     int c; 6     while(b>0) 7     { 8         c = a%b; 9         a = b;10         b = c;11     }12     if(a==1)return true;13     else return false;14 }15 int main()16 {17     int num,i;18     while(true)19     {20         printf("input the 32-bit int number you want to check:\n");21         scanf("%d",&num);22         for(i=2;i*i <= num;i++)23         if(!If_prime(num,i))break;24         if(i*i>num)printf("It`s a prime number.\n");25         else printf("It`s not a prime number.\n");26     }27 28     return 0;29 }