计算某天是一年中的第几天 很经典

int t_nMon;
int t_nDay;
cout << "输入月：";
cin >> t_nMon;
cout << "输入天：";
cin >> t_nDay;
int s_ndays = 0;

switch(t_nMon-1)
{
case 12:s_ndays += 31;
case 11:s_ndays += 30;
case 10:s_ndays += 31;
case 9:s_ndays += 30;
case 8:s_ndays += 31;
case 7:s_ndays += 31;
case 6:s_ndays += 30;
case 5:s_ndays += 31;
case 4:s_ndays += 30;
case 3:s_ndays += 31;
case 2:s_ndays += 28;
case 1:s_ndays += 31;
}

s_ndays = s_ndays + t_nDay;
cout << s_ndays <<endl;