为什么在不应该抛出该异常时抛出该异常？

Question

我有以下（非常简单的）控制台计算器，可以进行基本的圆计算：

using System;

namespace Circle
{
    class Program
    {
        /* Compute the area of a cricle given its radius. */
        public static double Area(double radius)
        {
            return Math.Pow(radius, 2) * Math.PI;
        }

        /* Compute the circumference of a circle given is radius. */
        public static double Circumference(double radius)
        {
            return radius * 2 * Math.PI;
        }

        /* Compute the diameter of a circle given its radius. */
        public static double Diameter(double radius)
        {
            return radius * 2;
        }

        /* Report the result. */
        public static string Result(double radius, double area, double circumference, double diameter)
        {
            return "- A circle whose radius is " + radius + " has the following properties: "
                    + "\n- Area: " + area.ToString("0.##") + "\n- Circumference: " + circumference.ToString("0.##")
                    + "\n- Diameter: " + diameter.ToString("0.##");
        }

        static void Main(string[] args)
        {
            double radius = 0;
            char choice;
            while (true)
            {
            Calculate:
                {
                    // 1. Get the radius from the user. 
                    Console.Write("- Enter the radius of the circle: ");
                    try
                    {  // verify the input is of numerical type 
                        radius = Convert.ToDouble(Console.ReadLine());
                        if (radius <= 0)  // check for negative values 
                        {
                            Console.WriteLine(" [Error] Radius must be a positive value!");
                            Console.WriteLine();
                            continue;  // restart from the next iteration without executing the rest of the statements 
                        } // end if 
                    }
                    catch (FormatException e)
                    {
                        Console.WriteLine(" [Error] " + e.Message);
                        Console.WriteLine(); // skip a line
                        continue;  // restart from the next iteration without executing the rest of the statements 
                    } // end catch 
                }
                // 2. Calculate the area, circumference, and diameter of the circle. 
                double area = Area(radius);
                double circumference = Circumference(radius);
                double diameter = Diameter(radius);
                // 3. Display the results. 
                Console.WriteLine(Result(radius, area, circumference, diameter));
            // 4. Ask the user whether to quit.
            Ask:
                {
                    Console.Write("- Do you wish to make another calculation [Y or N]? ");
                    choice = Convert.ToChar(Console.Read());
                }
                if (choice.Equals('Y') || choice.Equals('y'))
                {
                    goto Calculate; // return to the beginning of the Calculate block. 
                }
                else if (choice.Equals('N') || choice.Equals('n'))
                {
                    break; // exit 
                }
                else {
                    Console.WriteLine("Invalid choice! Press Y to continue or N to exit.");
                    goto Ask; // return to the beginning of the Ask block. 
                }
            }  // end while 
            Console.WriteLine("Thank you for using me. Have a nice day!");
            Console.WriteLine();
        } // end Main 
    }
}

计算后，程序会询问用户是否要进行另一次计算。如果用户输入 Y，程序会提示他们再次输入半径。如果用户输入 N，程序终止。

然而，有两个基本问题：

如果用户选择按Y进行另一次计算，程序会提示用户输入一个值，但也会执行catch块并抛出异常。这显示在示例输出中：

Enter the radius of the circle: 3

A circle whose radius is 3 has the following properties:

Area: 28.27

Circumference: 18.85

Diameter: 6

Do you wish to make another calculation [Y or N]? Y

Enter the radius of the circle: [Error] Input string was not in a correct format.

Enter the radius of the circle:

第二个问题是当用户输入 Y 或 N 以外的内容时，程序也会出现意外行为，如输出所示：

Enter the radius of the circle: 4

A circle whose radius is 4 has the following properties:

Area: 50.27

Circumference: 25.13

Diameter: 8

Do you wish to make another calculation [Y or N]? j Invalid choice! Press Y to continue or N to exit.

Do you wish to make another calculation [Y or N]? Invalid choice! Press Y to continue or N to exit.

Do you wish to make another calculation [Y or N]? Invalid choice! Press Y to continue or N to exit.

Do you wish to make another calculation [Y or N]?

我似乎无法弄清楚为什么会发生这两种情况。我怀疑这是我使用 goto 和 continue，但我说不出来。

Answer 1

问题在于您使用了 Read() 和 ReadLine()，以及如何将输入从 shell 发送到 Console 对象。

在控制台对象中，输入流（缓冲区）仅在按下 [Enter] 后加载。那时，Read() 将 return 字符串中的下一个未读字符，但 只有那个字符 。当随后调用 ReadLine() 时，它会转到换行符仍在等待的缓冲区，因此它立即 returns （在这种情况下）一个空字符串。随之而来的是欢闹。

补救留作 reader 的练习;)

Answer 2

问题是你的Convert.ToChar(Console.Read())。它从输入中读取一个字符，但在按下回车之前不会从控制台设置输入。所以 Console.Read() 正确地得到 'Y'，但是输入有一个 ENTER 排队，所以你的 Convert.ToDouble(Console.ReadLine()) 得到一个它试图转换的空字符串因此例外。

将 Convert.ToChar(Console.Read()) 更改为 Convert.ToChar(Console.ReadLine())，它工作正常。

您还应该摆脱 gotos 并摆脱异常陷阱 - 您应该改用 double.TryParse(...)。没有更多例外。

我重构了您的代码让您尝试 - 没有 gotos 也没有异常处理。

while (true)
{
    while (true)
    {
        Console.Write("- Enter the radius of the circle: ");
        double radius;
        if (double.TryParse(Console.ReadLine(), out radius) && radius > 0.0)
        {
            double area = Area(radius);
            double circumference = Circumference(radius);
            double diameter = Diameter(radius);
            Console.WriteLine();
            Console.WriteLine(Result(radius, area, circumference, diameter));
            break;
        }
        Console.WriteLine(" [Error] Radius must be a positive value!");
        Console.WriteLine();
    }
    string choice = "";
    while (true)
    {
        Console.Write("- Do you wish to make another calculation [Y or N]? ");
        choice = Console.ReadLine();
        if (new [] { "Y", "N", }.Contains(choice.ToUpper()))
        {
            break;
        }
        Console.WriteLine();
        Console.WriteLine("- Invalid choice! Press Y to continue or N to exit.");
    }
    if (choice.ToUpper() == "N")
    {
        break;
    }
    Console.WriteLine();
}
Console.WriteLine();
Console.WriteLine("- Thank you for using me. Have a nice day!");
Console.WriteLine();

为什么在不应该抛出该异常时抛出该异常？

Why Is This Exception Thrown When it Shouldn't Be?

c#

exception

console-application