#include"iostream"

using namespace std;

void main01() {

    //printf("hello_world\n");

    cout << "hello_world\n" << endl;//在c++里面输出

    system("pause");

}

//求圆的面积

//用面向过程的方法求解了圆形的面积

void main() {

    double r = ;

    double s = ;

    //printf("hello_world\n");

    cout << "请输入圆的半径：";

    cin >> r; //cin代表标准输入

    cout << "r的值是：" << r << endl;

    s = 3.14*r*r;

    cout << "圆形的面积是s=" << s << endl;

    system("pause");

}

//面向对象的思路解决这问题

class CirCle {

private:

    double m_s;

    double m_r;

    double m_c;

public:

    void setR(double r) {

        this->m_r = r;

    }

    double getR() {

        return this->m_r;

    }

    double getS() {

        return this->m_r * m_r * 3.14;

    }

    double getC() {

        return this->m_r *  * 3.14;

    }

};

int main() {

    CirCle c1, c2;

    double r,r2;

    cout << "输入c1圆的半径" ;

    cin >> r;

    c1.setR(r);

    cout << "c1圆的面积是" << c1.getS() <<endl;

    cout << "c1元的周长是" << c1.getC() << endl;

    cout << "输入c2圆的半径" ;

    cin >> r2;

    c2.setR(r2);

    cout << "c2圆的面积是" << c2.getS() << endl;

    cout << "c2元的周长是" << c2.getC() << endl;

    system("pause");

    return ;

}

#include "iostream"

using namespace std;

//定义命名空间

namespace namespaceA {

    int a = ;

}

namespace namespaceB {

    int a = ;

}

//使用命名空间

void main() {

    using namespace namespaceA;

    cout << a << endl;

    cout << namespaceB::a << endl;

    system("pause");

}