C++PrimerPlus中文第六版第7章编程练习答案

1、

#include<iostream>
using namespace std;

double computeHarmonicMean(double x, double y);
int main()
{
    double x, y;
    cout << "Enter two numbers(x!=0 and y!=0): ";
    bool valid;
    valid = (bool)(cin >> x >> y);
    while (!valid)
    {
        cin.clear();
        while (cin.get() != '\n');
        cout << "Enter invalid! enter again!\n";
        cout << "Please enter two numbers(x!=0 and y!=0): ";
        valid = (bool)(cin >> x >> y);
    }
    while (x != 0 and y != 0)
    {
        cout <<"Harmonic mean: " << computeHarmonicMean(x, y) << endl;
        cout << "Enter two numbers(x!=0 and y!=0): ";
        valid = (bool)(cin >> x >> y);
        while (!valid)
        {
            cin.clear();
            while (cin.get() != '\n');
            cout << "Enter invalid! enter again!\n";
            cout << "Please enter two numbers(x!=0 and y!=0): ";
            valid = (bool)(cin >> x >> y);
        }
    }

    cout << "x==0 or y==0 holds to quit\n";


}

double computeHarmonicMean(double x, double y)
{
    return 2.0 * x * y / (x + y);
}

2、