#include <stdio.h>

int main() {
   int array[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
   int sum, loop;
   float avg;

   sum = avg = 0;

   for(loop = 0; loop < 10; loop++) {
      sum = sum + array[loop];
   }

   avg = (float)sum / loop;

   printf("平均值为 %.2f", avg);   

   return 0;
}

平均值为 4.50

#include <stdio.h>

int main()
{
    int n, i;
    float num[100], sum = 0.0, average;

    printf("输入元素个数: ");
    scanf("%d", &n);

    while (n > 100 || n <= 0)
    {
        printf("Error! 数字需要在1 到 100 之间。\n");
        printf("再次输入: ");
        scanf("%d", &n);
    }

    for(i = 0; i < n; ++i)
    {
        printf("%d. 输入数字: ", i+1);
        scanf("%f", &num[i]);
        sum += num[i];
    }

    average = sum / n;
    printf("平均值 = %.2f", average);

    return 0;
}

输入元素个数: 4
1. 输入数字: 1
2. 输入数字: 2
3. 输入数字: 4
4. 输入数字: 8
平均值 = 3.75