7.1
#include<iostream> using namespace std; double tiaohe(double ,double ); void main71() { double a,b; cout<<"Plesase enter 2 number :"; cin>>a; cin>>b; if(a==0||b==0) cout<<" Wrong input"<<endl; else cout<<"tiaohe is "<<tiaohe(a,b)<<endl; system("pause"); } double tiaohe(double a,double b) { return 2.0*a*b/(a+b); }