练习20

#include <iostream>
using namespace std;


class Tree {
int ages;
public:
Tree(int n=0);
~Tree();
void grow(int years);
void age();
};


Tree::Tree(int n) {
ages = n;
}


Tree::~Tree() {
age();
}


void Tree::grow(int years) {
ages += years;
}


void Tree::age() {
cout << "这棵树的年龄为" << ages << endl;
}


int main()
{
    Tree t(12);


    t.age();
    t.grow(4);
return 0;
}