如何解决使用字符串的C#计算器
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;
}
}
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