求一个素数的c程序

#include<stdio.h>
#include<math.h>

int main()
{
    int num,i,a,stutas=0;
 
    scanf("%d",&num);
    a = sqrt(num);
 
    if(num<4)
        printf("the num is  a sushu\n");
    else
    {
        for(i=2; i<a; i++)
        {
             if((num%i)==0)
             {
                 printf("the num is not a sushu \n");
                 stutas = 1;                    //stutas很重要。
                 break;
              }
       }
   }
   if(stutas == 1)
       printf("the num is not a sushu \n");
   else
       printf("the num is a sushu \n");

    return 0;
}