c#使用什么循环

从技术上讲,你可以实现任何循环,但我建议while

 ...
 string answer1 = Console.ReadLine();

 while (answer1 != "yes" && answer1 != "no") {
   Console.WriteLine("Pardon me?");
   answer1 = Console.ReadLine();
 }
 ...

只是不断询问,而 answer1不是正确的.

编辑:正如Hogan在评论中建议的那样,我们应该对用户很好:让他/她在任何带有前导和尾随空格的寄存器中输入YES/no:

 ...
 // with Trim() and ToUpper() all "Yes", "   yes", "YES  " are OK
 string answer1 = Console.ReadLine().Trim().ToUpper();

 while (answer1 != "YES" && answer1 != "NO") {
   Console.WriteLine("Pardon me?");

   answer1 = Console.ReadLine().Trim().ToUpper();
 }
 ... 

编辑2:退出程序(请参阅注释中的其他问题),只需从以下位置返回Main:

 ...
 if (answer1 == "NO") {
   Console.WriteLine("Your loss"); 

   return; // return from Main will exit the program
 }