使用字符串的C＃计算器

问题描述

我需要在不使用任何库的情况下对字符串行进行算术运算。我已经尝试了以下代码-

string s = Console.ReadLine();

switch (s[1])
{
    case s[1] == "+":
        Console.WriteLine("Result: " + (s[0] + s[2]));
        break;
    case "-":
        Console.WriteLine("Result: " + (s[0] - s[2]));
        break;
    case "*":
        Console.WriteLine("Result: " + (s[0] * s[2]));
        break;
    case "/":
        if (s[2] != 0)
            Console.WriteLine("Result: " + (s[0] / s[2]));
        else
            Console.WriteLine("Indeterminate");
        break;
}

Console.WriteLine(s);

但是我不确定如何将字符串转换为char。

有什么办法可以使这项工作吗？我正在寻找任何建议或技巧。

解决方法

编译器会告诉您问题：

 CS0029 Cannot implicitly convert type 'string' to 'char'   

此错误发生在case语句中。它期望char，而不是string。 C＃中的字符串文字用双引号引起来，字符文字（char）用单引号引起来。

在第一个case语句中，您有s[1] == "+"。那里不应该有一个比较（switch case为您做到了）

switch (s[1]) // s[1] is of type char 
{
    case '+': 
        Console.WriteLine("Result: " + (s[0] + s[2]));
        break;
    case '-':
        Console.WriteLine("Result: " + (s[0] - s[2]));
        break;
    case '*':
        Console.WriteLine("Result: " + (s[0] * s[2]));
        break;
    case '/':
        if (s[2] != 0)
            Console.WriteLine("Result: " + (s[0] / s[2]));
        else
            Console.WriteLine("Indeterminate");
        break;
}

最后，您应该注意字符文字数字与其表示形式具有不同的数值。您应该解析字符以获得数字值。例如：

var value1 = int.Parse(s[0].ToString());
var value2 = int.Parse(s[2].ToString());

接下来，您将意识到您的计算器仅支持1位数字，并且您可能希望预先添加一些输入验证，以避免程序因无效输入而崩溃。

,

正如jeroenh提到的那样，问题是您在char情况下将string与switch进行比较，这是不允许的。您必须比较类似类型。

但是，最好先将输入字符串解析为适当的类型，然后再进行比较和数学运算，而不是依赖字符串中字符的索引。如果用户输入一个多位数的数字或在运算符周围添加空格，这可以使用户输入更加灵活。

例如：

// These are the allowed operators
var operators = new[] {'+','-','/','*'};

// Get user input
string s = Console.ReadLine();

// Find the first index of an operator
var operatorIndex = operators.Any(s.Contains)
    ? operators.Select(op => s.IndexOf(op)).Where(index => index > -1).Min()
    : -1;

// If no valid operators are present,give an error message to the user
if (operatorIndex < 0)
{
    throw new ArgumentException(
        $"Input doesn't contain a valid operator ({string.Join(",",operators)}).");
}

// Based on the operator position,find the portions of the string that
// represent the first number,the operator,and the second number.
var firstNumber = s.Substring(0,operatorIndex);
var operatorChar = s[operatorIndex];
var secondNumber = s.Substring(operatorIndex + 1);
        
int operand1,operand2;

// Try to parse the first and second number to integers. If either 
// of them are invalid,give an error message to the user
if (!int.TryParse(firstNumber,out operand1) ||
    !int.TryParse(secondNumber,out operand2))
{
    throw new ArgumentException(
        $"Input doesn't contain a valid integer on each side of the operator.");
}

// Now we can swich on the operator character and do math with the integers
switch (operatorChar)
{
    case '+':
        Console.WriteLine("Result: " + (operand1 + operand2));
        break;
    case '-':
        Console.WriteLine("Result: " + (operand1 - operand2));
        break;
    case '*':
        Console.WriteLine("Result: " + (operand1 * operand2));
        break;
    case '/':
        if (operand2 != 0)
            Console.WriteLine("Result: " + (operand1 / operand2));
        else
            Console.WriteLine("Indeterminate");
        break;
}

Console.Write("\nPress any key to exit...");
Console.ReadKey();

,

如果任务没有排除.Net中可用的命名空间，则可以根据需要调整Microsoft DotNet Documentation中的这个出色示例。

这是他们解释的代码片段：

String[] expressions = {
 "16 + 21","31 * 3","28 / 3","42 - 18","12 * 7","2,4,6,8" };

String pattern = @"(\d+)\s+([-+*/])\s+(\d+)";

foreach (var expression in expressions)
  foreach (System.Text.RegularExpressions.Match m in System.Text.RegularExpressions.Regex.Matches(expression,pattern)) 
  {
    int value1 = Int32.Parse(m.Groups[1].Value);
    int value2 = Int32.Parse(m.Groups[3].Value);
    switch (m.Groups[2].Value)
    {
      case "+":
        Console.WriteLine("{0} = {1}",m.Value,value1 + value2);
        break;
      case "-":
        Console.WriteLine("{0} = {1}",value1 - value2);
        break;
      case "*":
        Console.WriteLine("{0} = {1}",value1 * value2);
        break;
      case "/":
        Console.WriteLine("{0} = {1:N2}",value1 / value2);
        break;
    }
  }
// The example displays the following output:
//       16 + 21 = 37
//       31 * 3 = 93
//       28 / 3 = 9.33
//       42 - 18 = 24
//       12 * 7 = 84

使用正则表达式可以“保存”原始输入字符串的各个部分，并将其拆分为表达式的匹配值。

这是正则表达式的作用的图像：

正则表达式将您的字符串分成第一个数字的捕获组（可通过m.Groups[1]使用并保存到value1中），用于运算符的捕获组分为第2组和一个捕获组您的第二个号码进入第3组。

采用Console.ReadLine()输入并使用正则表达式，您可以获得类似的结果：

using System.Text.RegularExpressions;


//...

string expression = Console.ReadLine()

String pattern = @"(\d+)\s+([-+*/])\s+(\d+)";
 
foreach (Match m in Regex.Matches(expression,pattern)) 
{
  // As others have pointed out you need to parse your numbers:
  int value1 = Int32.Parse(m.Groups[1].Value);
  int value2 = Int32.Parse(m.Groups[3].Value);
  
  // Now we switch case the operator in Group 2
  switch (m.Groups[2].Value)
  {
    case "+":
      Console.WriteLine("{0} = {1}",value1 + value2);
      break;
    case "-":
      Console.WriteLine("{0} = {1}",value1 - value2);
      break;
    case "*":
      Console.WriteLine("{0} = {1}",value1 * value2);
      break;
    case "/":
      Console.WriteLine("{0} = {1:N2}",value1 / value2);
      break;
  }
}