fork的微妙问题1

/*
Author:Justinzhang
email:uestczhangchao@gmail.com
time:2012-8-30 22:17:23
desc：fork problem, from www.qshpan.com
*/

#include <stdio.h>
#include <stdlib.h>
int sum;
int main()
{
    int i = 0;
    sum = 0;
    fork();
    for(i=0; i<5; i++)
    {
        printf("%d\n",i);
        fflush(stdout);
        sum += i;
    }
    printf("sum = %d\n", sum);

    exit(0);
}