工具：计时器

代码如下

# include <bits/stdc++.h>
# include <windows.h>
# include <conio.h>
using namespace std ;
long long secs ;
int main ( )
{
	int h , m , s ;
	cout << "Timer V1.0\nBy Michael0727" << endl ;
	system ( "pause" ) ;
	system ( "cls" ) ;
	in : cout << "Input the time ( hh : mm : ss )" << endl << endl ;
	cin >> h >> m >> s ;
	if ( m >= 60 || s >= 60 )
	{
		system ( "cls" ) ;
		cout << "Illeagal !" << endl << endl ;
		goto in ;
	}
	secs = h * 3600 + m * 60 + s ;
	while ( -- secs )
	{
		system ( "cls" ) ;
		s -- ;
		if ( s == -1 )
		{
			m -- ;
			s = 59 ;
		}
		if ( m == -1 )
		{
			h -- ;
			m = 59 ;
		}
		cout << h << " : " << m << " : " << s << endl ;
		Sleep ( 1000 ) ;
	}
	int cnt = 0 ;
	while ( ! kbhit ( ) )
	{
		system ( "cls" ) ;
		cout << "Timeout !\a" << endl ;
		cnt ++ ;
		Sleep ( 1000 ) ;
	}
	cout << "Delay : " << cnt << " s" << endl ;
	return 0 ;
}