无法将类型“字符串”隐式转换为“int”错误

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Assignment2
{
class Program
{
    static void Main(string[] args)
    {
        int Value1,Value2,result,a;
        Console.Write("Enter Value 1: ");
        Value1 = Convert.ToInt32(Console.ReadLine());
        Console.Write("Enter Value 2: ");
        Value2 = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine("Choose an arithmetic operator:");

        Console.WriteLine("'t1. +(add)");
        Console.WriteLine("'t2. -(subtract)");
        Console.WriteLine("'t3. *(multiply)");
        Console.WriteLine("'t4. /(divide)");
        Console.Write("'t5. %(mod)");
        Console.Write("'n'n");
        a = Convert.ToInt32(Console.ReadLine());
        switch (a)
        {
            case"1":
                Console.WriteLine("Operator is: Add");
                result=Value1+Value2;
                Console.WriteLine("Result: "+result);
                break;
            case"2":
                Console.WriteLine("Operator is: Subtract");
                result=Value1-Value2;
                Console.WriteLine("Result: "+result);
                break;
            case"3":
                Console.WriteLine("Operator is: Multiply");
                result=Value1*Value2;
                Console.WriteLine("Result: "+result);
                break;
            case"4":
                Console.WriteLine("Operator is: devide");
                result=Value1/Value2;
                Console.WriteLine("Result: "+result);
                break;
            case"5":
                Console.WriteLine("Operator is: mod");
                result = Value1 % Value2;
                Console.WriteLine("Result: "+result);
                break;
        }
    }
}
}

有基本的 C#，在完成编码后，我尝试制作一个可以使用 Case 语句运行 5 个算术运算的程序。我发现了5个让我卡住的错误。并且输出将始终带有 2 个结果（即我选择添加。并且会出现2个输出，同时加减。有人可以帮助我吗？