程序代码：

#include<iostream>
using namespace std;
class D
{
    public:
    D()
    {d=0;}
    D(double i)
    {d=i;}
    void Print()
    {
        cout<<d<<endl;
    }
    private:
    double d;
};
void main()
{
    D d;
    d=20;
    d.Print();
}