Visual Studio 2015社区c#计算器代码错误

我写了一个测试示例代码，我有问题。代码的

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SEC3_LEC19 {
  class Program {
    static void Main(string[] args) {
      int x, y;
      string num1, num2, choice = "yes";
      char op;
      bool again = true;
      while (again) {
        Console.WriteLine("Enter two integers");
        // First Number
        Console.Write("Enter num1: ");
        num1 = Console.ReadLine();
        // Second Number
        Console.Write("Enter num2: ");
        num2 = Console.ReadLine();
        // The Operator
        Console.Write(
          "Enter the operation [+ - * /]: ");
        op = (char)Console.Read();
        if (int.TryParse(num1, out x)) {
          ;
        } else {
          Console.WriteLine(
            num1 + " is NaN val set to 0");
        }
        if (int.TryParse(num2, out y)) {
          ;
        } else {
          Console.WriteLine(
            num2 + " is NaN val set to 0");
        }
        switch (op) {
          case '+':
            Console.WriteLine(
              x + " + " + y + " = " + (x + y));
            break;
          case '-':
            Console.WriteLine(
              x + " - " + y + " = " + (x - y));
            break;
          case '*':
            Console.WriteLine(
              x + " * " + y + " = " + (x * y));
            break;
          case '/':
            if (y == 0) {
              Console.WriteLine(
                "Division by zero not allowed!");
            } else {
              Console.WriteLine(
                x + " / " + y + " = " + (x - y));
            }
            break;
          default:
            Console.WriteLine(
              "Operator Unrecognized");
            break;
        }
        // Offer user to try again
        Console.Write("Go again? [yes/no]: ");
        // Read user input [NOT WORKING]
        choice = Console.ReadLine();
        switch (choice.ToLower()) {
          case "yes":
            again = true;
            break;
          case "no":
            again = false;
            break;
          default:
            Console.WriteLine(
              "Unrecognized choice!");
            break;
        }
      }
      // **********************************************
      Console.WriteLine("Press any key to continue..");
      Console.ReadKey();
    }
  }
}

代码通过控制台使用while循环，要求用户输入两个数字，然后输入一个运算符，然后执行并显示计算结果。如果他们继续询问用户是否愿意再试一次。它使用choice = Console.ReadLine()语句。根据答案，代码要么继续while循环，要么跳出循环。不幸的是，编译器似乎跳过了选择部分，直接进入switch语句。在代码的顶部也有类似的语句，它们工作得很好。