#include<stdio.h>
int main(){
    int j,done;
    int n;

    scanf("%d",&n);

    for(j=2;j<n;j++){
         if(n%j==0){
            done=0;
         }
         else {
             done=1;
         }
    }
        if(done==0){
          printf("not");
       }
      else if(done==1){
        printf("is");
      }
      return 0;
 }
结果总是显示 is 怎么回事，
怎么修改比较好