//给出一个大于等于三的数判断是不是素数
 #include"stdio.h"
 #include"stdio.h"
 int main()
 {
     int i,n,flag;
     printf("please enter a number:\n");
     scanf("%d",&n);
     for(i=2;i<=sqrt(n);i++)
      {
      if(n%i==0)
      flag=1;                                                                                                                                                                                                                                                      
      break;
     }
     if(flag)
      printf("%d不是素数\n",n);
      else
      printf("%d是素数\n",n);
      return 0;
}