UVA 10235 - Simply Emirp : Solution

#include<bits/stdc++.h>
using namespace std;

bool mark[1000000];
void sieve()
{
    memset(mark,true,1000000);
    mark[1]=false;
    for (int i=4; i<1000000;i+=2)
        mark[i]=false;
    for (int i=3;i<1000;i+=2)
        if (mark[i])
            for (int j=i*i;j<1000000;j+=i*2)
                mark[j]=false;
    return;
}

int main()
{
    int n;
    sieve();
    while (scanf("%d",&n)==1)
    {
        int rev=0;
        int temp=n;
        while (temp)
        {
            rev=rev*10+temp%10;
            temp/=10;
        }
        if (mark[n])
        {
            if (mark[rev] && n!=rev) printf("%d is emirp.\n",n);
            else printf("%d is prime.\n",n);
        }
        else printf("%d is not prime.\n",n);
    }
    return 0;
}