如何修复“无法找到类型或命名空间名称”？

Question

这是我之前的问题https://codereview.stackexchange.com/questions/12165/efficency-in-c/12169的后续内容，我尽力使用BigIntegers代替ulongs，但我一定做错了。我是C＃的新手，我熟悉Java。这是我转换时的最佳镜头：

using System;

namespace System.Numerics{

      public class Factorial{

             public static void Main(){

             String InString = Console.ReadLine();

             BigInteger num = 0;

             BigInteger factorial = 1;

             try {
                 num = BigInteger.Parse(InString);
                 Console.WriteLine(num);
                 }
             catch (FormatException) {

                  Console.WriteLine("Unable to convert the String into a BigInteger");
            }



            for (BigInteger forBlockvar = num; forBlockvar > 1; forBlockvar--){

                     factorial *= forBlockvar;

            }

            Console.WriteLine("The Factorial for the Given input is:");

            Console.WriteLine(factorial);
    }
}
}

我收到了以下错误：

prog.cs(11,18): error CS0246: The type or namespace name `BigInteger' could not be found. Are you missing a using directive or an assembly reference?
prog.cs(13,18): error CS0246: The type or namespace name `BigInteger' could not be found. Are you missing a using directive or an assembly reference?
prog.cs(26,22): error CS0246: The type or namespace name `BigInteger' could not be found. Are you missing a using directive or an assembly reference?

这个错误是什么意思，我该如何解决？

Answer 1

您需要在System.Numerics.dll中添加引用（右键单击Solution Explorer中的References并选择Add Reference）。

另外，放入using System.Numerics而不是让你的方法命名空间（即将其命名为代码库更具描述性）。