小朋友学C++（9）：构造函数的默认参数

#include <iostream>
using namespace std;
class Rectangle
{
private:
    int width;
    int height; 
public:
    Rectangle(int w = 0, int h = 0)
    {
        cout << "Constructor method is invoked!" << endl;
        width = w;
        height = h;
    }
    int area()
    {
        return width * height; 
    }
};
int main(int argc, char** argv) 
{
    Rectangle rec1;
    cout << "Area of rec1 is : " << rec1.area() << endl;
    Rectangle rec2(5);
    cout << "Area of rec2 is : " << rec2.area() << endl;
    Rectangle rec3(5, 10);
    cout << "Area of rec3 is : " << rec3.area() << endl;
    return 0;   
}

Constructor method is invoked!
Area of rec1 is : 0
Constructor method is invoked!
Area of rec2 is : 0
Constructor method is invoked!
Area of rec3 is : 50