C primer plus（编程练习）file-9.11-4

/* 9.11-4 设计一个函数 ，接收两个 double 类型的参数，返回这两个参数的平均值。驱动测试调用函数 */#include <stdio.h>double Harmonic_mean(double, double);//调和平均数的函数声明int main(void){    double x = 3.90237;    double y = 8.00001;    Harmonic_mean(x, y);//调用 Harmonic_mean() 函数    printf("Harmonic_mean = %f", Harmonic_mean(x, y));    putchar('\n');    return 0;}//函数定义double Harmonic_mean(double x, double y){    double a, b;    double average_value;    a = 1.0/x;    b = 1.0/y;    average_value = (a + b)/2.0;    return (1.0/average_value);}