计算一个数组元素的平均值：

#include <stdio.h>

int main()

{ int numbers[] = {5, 7, 2, 9, 1};

int length = sizeof(numbers) / sizeof(numbers[0]);
int sum = 0;
float average;

for (int i = 0; i < length; i++) {
    sum += numbers[i];
}

average = (float)sum / length;
printf("平均值为：%.2f\n", average);

return 0;

}