需要我的第一个计算器的帮助 [英] Need assistance with my first calculator

问题描述

所以我刚开始学习编码，大约花了1个星期.我想尝试制作一个具有+和-的计算器，但无法弄清楚如何让用户选择他想使用的东西，有没有人可以帮助我呢?这是代码.

so i just started learning coding, been going at it for about 1 week. i wanted to try and make a calculator that does + and - but cant figure out how to let the user choose what he wants to use, is there anyone that can help me with that? here is the code.

        int x;
        int y;
        Console.WriteLine("Welcome to my calculator program!");
        Console.WriteLine("This calculator for now can only do + and -");
        Console.WriteLine("If x is highter than y it will do - and if x is lower than y it will do +");

        Console.WriteLine("pls write in you x");
        x = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine("pls write in your y");
        y = Convert.ToInt32(Console.ReadLine());

        if (x > y)
        {
            Console.WriteLine("you chose to use minus");
            int sum = x - y;
            Console.WriteLine("result: {0}", sum);
            Console.WriteLine("Press a key to exit");
            Console.ReadLine();
        }
        else
        {
            Console.WriteLine("you chose to use plus");
            int sum1 = x + y;
            Console.WriteLine("result: {0}", sum1);
            Console.WriteLine("Press a key to exit");
            Console.ReadLine();
        }


     }
}

}如您所见，如果x i小于y则使用+，如果x大于y则使用-.我知道如何使其工作的唯一方法.

} as you can see is just used + if the x i lower than y and - if the x is greater than y. the only way i knew how to make it work.

推荐答案

已经回答了幼稚的方法(询问用户).但是，您实际上可能想要实现的是编写一个功能强大的计算器，用户在其中输入 2 + 3 之类的字符串，然后程序会简单地给出答案.您希望编写一个解释器.

The naive approach (ask the user) has been answered. But what you probably actually want to achieve is write a full-fledged calculator where the user enters a string like 2+3 and the program simply gives the answer. You're aspiring to write an interpretor.

考虑一下，您将必须执行三个任务:

If you think about it, you will have to perform three tasks:

• 扫描用户输入，并将其转换为一系列标记.这是将字符串"2 + 3"转换为令牌系列值2的整数"，加运算符"，值3的整数"
• 解释令牌以计算结果

您在输入上施加的约束越多(例如，如您所说，仅允许+和-开头)，代码将越简单(如果无法根据您设定的规则解释输入，则失败)).

The more constraints you place on the input (e.g. as you said, only allow + and - to start with), the simpler the code will be (just fail if the input can not be interpreted according to the rules you set out).

如果您想更深入地研究，可以在此主题上找到许多资源.我很喜欢阅读这一系列博客文章(作者使用Python，但是原理保持不变)

If you want to dig deeper, there's numerous resources available on this subject. I enjoyed reading this series of blog posts (the author uses Python, but the principles remain the same).

最后，您会发现您想做的许多事情已经实现.有可用的库已经解析和评估数学表达式(示例: NCalc ，

In the end you will discover that much of what you are trying to do has already been achieved. There are libraries available that already parse and evaluate mathematical expressions (examples: NCalc, Mathos).

最后，Roslyn允许您轻松解析任何C#表达式，因此它也可以用于构建一个简单的计算器，如下所示:

On a final note, Roslyn allows you to parse any C# expression easily, so it can also be used to build a simple calculator, like this:

class Program
{
    static void Main(string[] args)
    {
        CSharpReplAsync().Wait();

    }

    private static async Task CSharpReplAsync()
    {
        Console.WriteLine("C# Math REPL");
        Console.WriteLine("You can use any method from System.Math");

        var options = ScriptOptions.Default
            .AddImports("System", "System.Console", "System.Math");

        var state = await CSharpScript.RunAsync("WriteLine(\"Hello from Roslyn\")", options);

        while (true)
        {
            Console.Write("> ");
            string expression = Console.ReadLine();
            if (string.IsNullOrEmpty(expression))
                break;
            try
            {
                state = await state.ContinueWithAsync(expression, options);
                if (state.ReturnValue != null)
                    Console.WriteLine(state.ReturnValue);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}

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