错误：在标准运算符>>< char中没有匹配“operator ==” [英] Error: No match for 'operator==' in standard operator>><char

问题描述

这里是一个解释（如在教程中）示例代码应该做什么：

，我们如何编写一个for循环，输出每个数字从1到100 ，但如果用户输入字母q，则停止？我们可以很容易地使用while循环，并使用我们上面学到的，使它相当小，但让它在一个for循环

当我运行它，我得到一个错误没有匹配的'operator =='...。现在我研究了网络和SO本身，但所有只是似乎有涉及概念，我还没有学到的高级答案。

我提供了代码，一些我研究的链接。在其中一个网站上，它说是的，基本上在C可以' t使用 == 比较字符串。在其他网站他们谈到超载运营商，我也研究了，但是只是困惑我更多。在 SO类似的问题上，一个人建议使用双引号，而不是单引号，但我知道这不会在我的情况下工作，因为我使用 char 而不是 const char 或 string 。我跑了，我的怀疑证实了。它给出一个错误：从const char到char的转换无效

所以基本上我的问题是： / p>

本教程中使用的代码有什么问题，以及可以防止出现错误的替代方法是什么？

  #include< iostream> 
 
 int main（）
 {
 int i = 0; 
 char input =''; 
 for（i = 1; i <= 100; ++ i）
 {
 if（（std :: cin>> input）=='a'）
 {
 break; 
} 
 
} 
 
 return 0; 
} 
  

解决方案

  std :: cin>>输入; 
  

返回对 std :: cin 这不奇怪，不能与 char 比较。您可能想要

  if（std :: cin>> input&&& input =='a'）
  

或更好，

  if（！（std :: cin>> input）|| input =='a'）
  

$ b b

如果读取输入失败，它也会中断。

Here is an explanation (as in the tutorial) of what the example code was supposed to do:

As a rather contrived example, how would we write a for loop that outputs every number from 1 to 100, but stops if the user enters the letter q? We could easily do it with a while loop, and use what we learnt above to make it quite small, but lets do it in a for loop

When I run it, I get an error "No match for 'operator=='...". Now I researched on the net and on SO itself, but all just seem to have advanced answers involving concepts which I have not yet learned.

I have provided the code and also some of the links where I researched. On one of the sites it says that "Yes, basically in C you can't use == to compare strings". On another site they spoke about overloading operators, which I also then researched, but that just confused me even more. On a similar problem here on SO one guy suggested using double quotes instead of single quotes, but I knew that would not work in my case since I used a char and not a const char or string. And I ran it and my suspicions were confirmed. It gave an error: "Invalid conversion from const char to char"

So basically my question is this:

What is wrong with this code used in the tutorial, and what are the alternatives to prevent getting an error?

#include <iostream>

int main()
{
    int i = 0;
    char input = ' ' ;
    for (i=1; i<=100; ++i)
    {
        if ((std::cin >> input) == 'a')
        { 
            break;
        }

    }

    return 0;
}

解决方案

std::cin >> input;

returns a reference to std::cin which, unsurprisingly, cannot be compared to a char. You probably want

if (std::cin >> input && input == 'a')

or even better,

if (!(std::cin >> input) || input == 'a')

which will also break if reading input fails.

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