1 #include <stdio.h>
 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 }