偶数-两个素数之和

用程序证明：一个偶数总能表示为两个素数之和

#include <stdio.h>
int primer_number(int num)
{
    int a, flag;
    flag=1;
    for (a=2; a<=num/2; a++)
    {
        if (num%a==0)
        {
            flag=0;
            continue;
        }
    }
    return flag;
}
int main()
{
    int a, i, num;
    scanf("%d", &num);
    if (num%2!=0)
    {
        printf("请输入一个偶数\n");
        return 0;
    }
    else
    {
        for (a=2; a<num/2; a++)
        {
            i=num-a;
            if (primer_number(a)==1 && primer_number(i)==1)
            {
                printf("%d=%d+%d\n", num, a, i);
            }
        }
        return 0;
    }
    return 0;
}