choosesubject(网上找的，仅自用，非原创)

using System;
class ChooseSubject
{
static void Main()
{
int i;
string str;
Console.WriteLine ("Please choose your favorite subjects:-1 is quit.");
Console.WriteLine ("1.Chinese.");
Console.WriteLine ("2.Maths.");
Console.WriteLine ("3.English.");
Console.WriteLine ("4.Physical.");
Console.WriteLine ("-1 is quit.");
do
{
str=Console.ReadLine ();
i=Int32.Parse (str);
switch(i)
{
case 1:
Console.WriteLine ("You like chinese very much.");
break;
case 2:
Console.WriteLine ("You like maths very much.");
break;
case 3:
Console.WriteLine ("You like english very much.");
break;
case 4:
Console.WriteLine ("You like physical very much.");
break;
case -1:
break;
default:
Console.WriteLine ("I‘m sorry.You can‘t choose this subject.");
break;
}

}while(i!=-1);
Console.WriteLine ("Byebye!");
}
}