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!");     } }