试着做一个计算器答案

【问题标题】：Trying to make a calculator试着做一个计算器
【发布时间】：2022-01-09 11:45:42
【问题描述】：

所以基本上每当我尝试更改 while 循环内的变量“restart”时，它都会给我一个错误，提示“无法在此范围内声明名为 'restart' 的本地或参数，因为该名称用于封闭的本地定义本地或参数的范围”。如果有人知道如何解决这个问题，请告诉我


public class Program
{
    public static void Main()
    {
        bool restart = true;
        while (restart == true)
        {
            Console.WriteLine("please enter Multiply, Divide, Add Or Subtract");
            string Method = Console.ReadLine();
            if (Method == "Add")
            {
                Console.WriteLine("Please Enter First Number");
                double numberOne = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("Please Enter The Second Number");
                double numberTwo = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine(numberOne + numberTwo);
                Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
                bool restart = Convert.ToBoolean(Console.ReadLine());
            }
            else if (Method == "Subtract")
            {
                Console.WriteLine("Please Enter First Number");
                double numberOne = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("Please Enter The Second Number");
                double numberTwo = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine(numberOne - numberTwo);
                Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
                bool restart = Convert.ToBoolean(Console.ReadLine());
            }
            else if (Method == "Multiply")
            {
                Console.WriteLine("Please Enter First Number");
                double numberOne = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("Please Enter The Second Number");
                double numberTwo = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine(numberOne * numberTwo);
                Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
                bool restart = Convert.ToBoolean(Console.ReadLine());
            }
            else if (Method == "Divide")
            {
                Console.WriteLine("Please Enter First Number");
                double numberOne = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine("Please Enter The Second Number");
                double numberTwo = Convert.ToDouble(Console.ReadLine());
                Console.WriteLine(numberOne / numberTwo);
                Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
                bool restart = Convert.ToBoolean(Console.ReadLine());
            }
            else
            {
                Console.WriteLine("error found");
                Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
                bool restart = Convert.ToBoolean(Console.ReadLine());
            }
        }
    }
}```

【问题讨论】：

取出bool restart = Convert.ToBoolean(Console.ReadLine());中的bool。当该变量在外部范围内声明时，您正试图在范围内声明一个 new 变量。
另请注意，您在每个 if 块中重复最后两行。你可以把它移到最后一个else之外。
@DStanley 谢谢，但它必须在每个 if 块之后我相信感觉 else 只是为了如果你做的事情不是“加、乘、减或除”
@Gh0ST：D 斯坦利是对的。您在每个“if”分支中都有相同的代码，因此代码无论如何都会运行。您可以（并且应该）在 else 语句的右大括号之后移动这两行。为了可维护性，避免在应用程序的不同部分重复相同的代码很重要（如果您在一堆地方重复的一行中有错误，则必须找到并修复所有这些地方）。
@EricJ。谢谢你，我现在明白他们的意思了

标签： c# while-loop calculator

【解决方案1】：

让我们看看这部分代码：

bool restart = true;
while (restart == true)
{
    // Some stuff omitted...
    bool restart = Convert.ToBoolean(Console.ReadLine());
}

你重新声明restart。相反，您应该像这样分配它（在第一次声明变量后使用变量时将bool 关闭）：

restart = Convert.ToBoolean(Console.ReadLine());

【讨论】：

【解决方案2】：

你需要这样的东西：

    bool restart = true;
    while (restart)
    {
        Console.WriteLine("please enter Multiply, Divide, Add Or Subtract");
        string method = Console.ReadLine();
        if (new[] { "Multiply", "Divide", "Add", "Subtract" }.Contains(method))
        {
            Console.WriteLine("Please Enter First Number");
            double numberOne = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("Please Enter The Second Number");
            double numberTwo = Convert.ToDouble(Console.ReadLine());
            if (method == "Add")
            {
                Console.WriteLine(numberOne + numberTwo);
            }
            else if (method == "Subtract")
            {
                Console.WriteLine(numberOne - numberTwo);
            }
            else if (method == "Multiply")
            {
                Console.WriteLine(numberOne * numberTwo);
            }
            else if (method == "Divide")
            {
                Console.WriteLine(numberOne / numberTwo);
            }
            Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
            restart = Convert.ToBoolean(Console.ReadLine());
        }
        else
        {
            Console.WriteLine("error found");
            Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
            restart = Convert.ToBoolean(Console.ReadLine());
        }
    }

或者这个：

    Dictionary<string, Func<double, double, double>> operations =
        new Dictionary<string, Func<double, double, double>>()
        {
            { "Add", (x, y) => x + y },
            { "Subtract", (x, y) => x - y },
            { "Multiply", (x, y) => x * y },
            { "Divide", (x, y) => x / y },
        };
    
    bool restart = true;
    while (restart)
    {
        Console.WriteLine($"Please enter one of: {String.Join(", ", operations.Keys)}");
        string method = Console.ReadLine();
        if (operations.ContainsKey(method))
        {
            Console.WriteLine("Please Enter First Number");
            double numberOne = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("Please Enter The Second Number");
            double numberTwo = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine(operations[method](numberOne, numberTwo));
        }
        else
        {
            Console.WriteLine("error found");
        }
        Console.WriteLine("Would You Like To Use The Calculator Again? (true = yes, false = no)");
        restart = Convert.ToBoolean(Console.ReadLine());
    }

【讨论】：

你有一些代码重复:-)（见 cmets）
我不相信new[] { "Multiply, Divide, Add Or Subtract" }.Contains(method) 做你想做的事。
@EricJ。 - 消除所有重复！ :-)