C#语言，从键盘输入一个年份和一个月份，判断该月是多少天！

("请输入一个年份：");
int year = Convert.ToInt32(());
("请输入一个月份：");
int month = Convert.ToInt32(());
switch (month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12: ("该月有31天！"); break;
case 4:
case 6:
case 9:
case 11: ("该月有30天！"); break;
case 2:
if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
{
("今年是闰年！有29天！");
}
else
{
("今年是平年！有28天！");
}
break;
default: ("您输入的月份错误！"); break;
}