c# - 为什么会出现 Invalid Expression Term "String"？

Question

我认为错误与 If 语句有关，但我尝试搜索错误，大多数问题是由语法错误引起的，这对我来说似乎不是这种情况。预先感谢您的帮助。

using System;

namespace FirstConsoleProjectSolution
{

  class MainClass
  {

    public static void Main (string[] args) // this is a method called "Main". It is called when the program starts.
    {
        string square;
        string cylinder;

        Console.WriteLine ("Please enter a shape");

        if (string == square) { 

            double length;
            double width;
            double height;

            Console.WriteLine ("Please enter length");
            Console.ReadLine (Convert.ToDouble ());

            Console.WriteLine ("Please enter width");
            Console.ReadLine (Convert.ToDouble ());

            Console.WriteLine ("Please enter height");
            Console.ReadLine (Convert.ToDouble ());

            Console.WriteLine ("Your total volume is" + length * width * height);
        }

        if (string == cylinder) {

            double areaOfBase;
            double height;

            Console.WriteLine ("Please enter area of base");
            Console.ReadLine (Convert.ToDouble ());

            Console.WriteLine ("Please enter height");
            Console.ReadLine (Convert.ToDouble ());

            Console.WriteLine ("Your total volume is" + areaOfBase * height);

        }
    }

  }

}   

Answer 1

那是因为这个声明:

if (string == square) {

string 关键字表示一种数据类型，无法比较数据类型和字符串。

您打印出的消息表明您正在尝试输入某些内容，但没有输入。我认为您正在尝试做类似的事情:

Console.WriteLine ("Please enter a shape");
string shape = Console.ReadLine();
if (shape == "square") {
  ...

---

稍后在代码中，当您尝试输入数字时，您将使用这样的代码来解析字符串并将其放入变量中:

length = Convert.ToDouble(Console.ReadLine());