C# 运算符“==”不能应用于“char”和“string”类型的操作数
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原文地址: http://stackoverflow.com/questions/19205107/
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Operator ‘==’ cannot be applied to operands of type ‘char’ and ‘string’
提问by TargetofGravity
I'm working on a self directed simple program to practice concepts I've learned thus far. My project is related to chess, in this case specifically the board (columns a-h and rows 1-8). The user is asked for the current location of a specific chess piece hopefully entered as a letter for the column followed by a number for the row. To validate this it made sense to me to first check if this value was entered as a string of two characters, otherwise what is entered is already incorrect. I then converted the entered string to lower case characters before comparing it with my list of acceptable array elements.
我正在开发一个自我指导的简单程序来练习我迄今为止学到的概念。我的项目与国际象棋有关，在这种情况下特别是棋盘（ah 列和 1-8 行）。用户被要求输入特定棋子的当前位置，希望输入为列的字母后跟行的数字。为了验证这一点，我首先检查这个值是否作为两个字符的字符串输入是有意义的，否则输入的内容已经不正确。然后，在将输入的字符串与可接受的数组元素列表进行比较之前，我将输入的字符串转换为小写字符。
From searching this siteI get the impression that a string stores its characters as an array and using the charproperty of string you would be able to pull off the first character thus comparing char to char. I have not yet found anything specific enough in my searches to really give me a good understanding of what is happening. Thisis the closest option I've come across which I didn't feel was applicable to this case. Any insight would be appreciated.
通过搜索此站点，我得到的印象是字符串将其字符存储为数组，并使用字符串的char属性，您将能够提取第一个字符，从而将 char 与 char 进行比较。在我的搜索中，我还没有找到任何足够具体的东西，让我真正了解正在发生的事情。这是我遇到的最接近的选项，我认为它不适用于这种情况。任何见解将不胜感激。
The code that follows produces the following error.
下面的代码会产生以下错误。
Operator ‘==' cannot be applied to operands of type ‘char' and ‘string'
运算符“==”不能应用于“char”和“string”类型的操作数
private char[] gridColumns = new char[] { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', };
private void createMoveButton_Click(object sender, RoutedEventArgs e)
{
// Assigns text box input to associated private fields
this.gameId = this.gameIdTextBox.Text;
this.playerId = this.playerIdTextBox.Text;
this.gamePiece = this.gamePieceTextBox.Text;
this.currentLocation = this.currentLocationTextBox.Text;
this.targetLocation = this.targetLocationTextBox.Text;
// Current location should only ever be 2 characters, ensure from the start this is true.
if (currentLocationTextBox.Text.Length == 2)
{
// Converts contents of currentLocationTextBox to lower case characters for comparison.
string cl = currentLocation.ToLowerInvariant();
// Iterates through my array of possible column choices
for (int i = 0; i < gridColumns.Length; i++)
{
Char.ToLowerInvariant(currentLocationTextBox.Text[0]);
// Trying to compare the first character of my string to the char element of my array.
if (cl[0] == gridColumns[i])
{
//TODO
}
}
}
else
{
MessageBox.Show("Check your starting location. It needs to be a lower case character variable (a-h) followed by a number (1-8)");
}
}
采纳答案by Dweeberly
Unlike C, a string and an array of char are different. A string in C# can be viewed as an array of char but you should consider them different, therefore the '==' comparison isn't appropriate. One easy way to see this is with the following simple expression
与 C 不同，字符串和字符数组是不同的。C# 中的字符串可以被视为一个字符数组，但您应该将它们视为不同的，因此“==”比较是不合适的。看到这一点的一种简单方法是使用以下简单表达式
if ("a" == 'a') { /* do something */ } // ERROR!
It looks like it should work but it generates the same error you are seeing, because it is trying to compare the string "a" to the char 'a'. In your example code the Text property of your textbox control is of type string.
看起来它应该可以工作，但它会产生与您看到的相同的错误，因为它试图将字符串“a”与字符“a”进行比较。在您的示例代码中，文本框控件的 Text 属性是字符串类型。
The string class has an indexer that allows you to treat a string as an array of char, but it's usually better (simpler) to use one of the many string methods to accomplish your goal. Consider this:
string 类有一个索引器，它允许您将字符串视为字符数组，但使用众多字符串方法之一来实现您的目标通常更好（更简单）。考虑一下：
var gridcolumns = "abcdefgh";
var gridrows = "12345678";
var input = "a1"; // column row
var col = gridcolumns.IndexOf(input[0]); // 0 -7
var row = gridrows.IndexOf(input[1]); // 0 -7
In the code you gave I don't see a line that would generate the error you provided. The following line serves no purpose
在您提供的代码中，我没有看到会生成您提供的错误的行。以下行没有用
Char.ToLowerInvariant(currentLocationTextBox.Text[0]);
Because you are not assigning the returned value to a variable, plus 'cl' already contains the lowercasing of that particular value.
因为您没有将返回值分配给变量，所以 plus 'cl' 已经包含该特定值的小写。
This line
这条线
if (cl[0] == gridColumns[i])
should not generate the error because both items are of type char.
不应产生错误，因为这两个项目都是 char 类型。
回答by Nikhil Agrawal
I ran your program and it works fine. I think problem is some place else.
我运行了你的程序，它运行良好。我认为问题出在其他地方。
回答by Szymon
Try to use this comparison:
尝试使用此比较：
(cl.ToCharArray())[0] == gridColumns[i]
回答by tinstaafl
Looping through the array just to see if an element is contained in it is kind of overkill when an array has a .Contains method. Something like this without the for loop should work:
当数组具有 .Contains 方法时，循环遍历数组只是为了查看其中是否包含元素是一种矫枉过正。没有 for 循环的类似这样的事情应该可以工作：
if (gridColumns.Contains(cl[0]))
{
//TODO
}
回答by Michael M.
Dweeberly's answer when applied... and shortened: Answer: Change the single quotes to double-quotes.
应用时 Dweeberly 的答案......并缩短：答案：将单引号更改为双引号。
My reasoning: Assume the following code:
我的推理：假设以下代码：
string IAmAString;
// set string to anything
IAmAString = "Q";
if (IAmAString == 'Q')
{
// do something, but never gets here because "Q" is a string, and 'Q' is a char
// Intellisense gives error on the if statement of
//
// "Operator '==' cannot be applied to operands of types 'string' and 'char'"
//
// because C# is a strongly typed language, and the '==' is not by
// default (in VS2012) overloaded to compare these two different types.
// You are trying to compare a string with something that
// is not-string, and C# is trying to let you know
// that that is not going to work.
}
It is fixed by changing the quotes to double-quotes. C# definitely seems to consider single quotes around a single character to be Char, and not string.
它通过将引号更改为双引号来修复。C# 似乎肯定将单个字符周围的单引号视为 Char，而不是字符串。
just change the quotes within the if statement:
只需更改 if 语句中的引号：
IAmAString = "Q";
if (IAmAString == "Q")
{
// does whatever is here within reason; "Q" is a string and "Q" is a string
}
At least this worked for me, and that's my 'quick' (where 'q' != "q") explanation of why.
Getting back to work...
至少这对我有用，这就是我对原因的“快速”（其中“q”！=“q”）解释。
回去工作...
