qt命名空间演示

#ifndef CIR_H
#define CIR_Hnamespace cir {double PI=3.141592653;//获取圆行周长double getLenthOfCircle(double radius){return 2*PI*radius;}//获取圆形面积double getAreaOfCircle(double radius){return PI*radius*radius;}}
#endif // CIR_H

#include <iostream>
#include "cir.h"
using namespace std;int main()
{double myRadius = 5;cout<<"lenth:"<<cir::getLenthOfCircle(myRadius)<<endl;;cout<<"Area:"<<cir::getAreaOfCircle(myRadius)<<endl;cout << "Hello World!" << endl;return 0;
}