递归追溯退出

#include <iostream>

using namespace std;

void countdown(int n);

extern int main01()
{
    countdown(4);
    return 0;
}

void countdown(int n)
{
    cout << "Couting down ... " << n << " \t(n at" << &n << ")" << endl;
    if(n > 0)
    {
        countdown( n - 1 );
    }
    cout << n << " : Kaboom!" << " \t\t(n at" << &n << ")\n";
}