01c++学习

#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 ;
}

c++中的命名空间

#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");
}