程序代码：

//average_2.c -- 输入三个实数，并求其平均值
#include <stdio.h>
int main(void)
{
    float num[3];
    int i, sum = 0;

    for (i=0; i<3; i++) {
        printf("Input a number to num[%d]:", i);
        scanf("%f", &num[i]);
        sum = sum + num [i];
    }
    printf("%d", i);
    printf("The average is %f\n", sum/i);

    return 0;
}