请具体分析一下这个定时关机程序

#include
#include
using namespace std;
int main()
{
int i;
cout << "1、关机" << endl
<< "2、重启" << endl
<< "3、注销" << endl
<< "4、休眠" << endl
<< "5、取消" << endl;
cin >> i;
switch (i)
{
case 1: {
int j;
cout << "1、关机" << endl
<< "2、定时关机" << endl
<< "3、取消定时关机" << endl
<< "4、取消" << endl;
cin >> j;
switch (j)
{
case 1:
system("shutdown -s -t 0");
break;
case 2: {
int t;
cout << "1、30分钟后关机" << endl
<< "2、60分钟后关机" << endl
<< "3、90分钟后关机" << endl
<< "4、120分钟后关机" << endl
<< "5、取消" << endl;
cin >> t;
switch (t)
{
case 1:
system("shutdown -s -t 1800");
break;
case 2:
system("shutdown -s -t 3600");
break;
case 3:
system("shutdown -s -t 5400");
break;
case 4:
system("shutdown -s -t 7200");
break;
case 5:
return 0;
default:
return 0;
}
break;
}
case 3:
system("shutdown -a");
break;
case 4:
return 0;
default:
return 0;
}
break;
}
case 2:
system("shutdown -r");
break;
case 3:
system("shutdown -l");
break;
case 4:
system("shutdown -h");
break;
case 5:
return 0;
default:
return 0;
}
return 0;
}

分析什么呢？就是shutdown关机指令不同参数