作法 : 質數判斷...

/******************************************************/

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int math[5200]={0};
int p;
int prime()
{
  char num[100000]={0};
  int a,b,m=0;
 for(a=2;a<50000;a++)  
      if(num[a]==0)  
        {  
           math[m]=a;  
           m++;  
           for(b=2;a*b<=50000;b++)  
             num[a*b]=1;  
        }
   return m;
}
int primeJudge (int num)
{
   int a,yes=0,s=(int)sqrt(num);
   for(a=0;a<p&&math[a]<=s;a++)
      if(num%math[a]==0)
         {yes=1;break;}
   if(yes==0)
      return 1;
   else
      return 0;  
}
int change (int num)
{
   int n=0;
   while(num)
      {
        n=n*10+num%10;
        num/=10;
      }
   return n;
}
main()
{
 p=prime();
 int n;
 while(scanf("%d",&n)==1)
     {
       if(n==1) break;
       int yes1=primeJudge(n),emirp=change(n);
       int yes2=primeJudge(emirp);
       if(yes1==1&&yes2==1&&n!=emirp)
          printf("%d is emirp.\n",n);
       else if((yes1==1&&yes2==0)||(yes1==1&&yes2==1&&n==emirp))
          printf("%d is prime.\n",n);
       else
          printf("%d is not prime.\n",n);
     }
 return 0;  
}