如何将字符添加到字符串中

首先，您应该用足够的占位符字符初始化gatherguess：

auto hangman = std::string{};
std::cin >> hangman;
auto gatherguess = std::string{hangman.size(), '_'};

现在，您可以简单地覆盖"_"字符。

auto pos = hangman.find(guess)
if(pos != std::string::npos) {
    // ...
    do {
        gatherguess[pos] = guess;   // overwrite
        pos = hangman.find(guess, pos); // find next ocurrence
    } while(pos != std::string::npos)
    // ...
}

我对您的代码进行了一些更改。它包含一些建议作为评论。

//#include <stdio.h> // Do not include a library if you don not use it, because it makes the performance worse.
//#include <string> // Do not include a library if you don not use it, because it makes the performance worse.
#include <iostream>     // std::cout
//#include <stdio.h> // It is pointless to include a library twice.
//#include <string.h>
//#include <iostream>     // std::cout
//#include <algorithm>    // std::for_each
//#include <vector> // Do not include a library if you don not use it, because it makes the performance worse.
//#include <set> // Do not include a library if you don not use it, because it makes the performance worse.
#include <string>
bool isitdone(const std::string& foo, const std::string& hang){ // Passing argument by const reference makes performance much better.
    return foo == hang ? true : false ; // Indenting makes the code much more readable.
}
int main(){
    const int N=10; // Store constant number in constant variable, because you can change its' value later easily.
    std::string hangman;
    char guess;
    std::string gatherguess; //Get the letters guessed.
    std::cin >> hangman; //Player enter the word to guess.
    bool checkstatement; // Check to see if game is over.
    for(int i =0; i < N; ++i)
    {
        std::cin >> guess; //Individual characters to guess
        std::string doo;
        int wordsin;
        doo = hangman;
        int y;
        if(doo.rfind(guess) != std::string::npos)
        {
            std::cout << "Right " << guess << " Is in the word"  << std::endl;
            std::cout << std::endl;
            checkstatement = isitdone(gatherguess,doo);// I want to add guess char into gatherguess
            //then check to see if gatherguess is equal to the word then the game will be complete
            if(checkstatement == true)
            {
                return 0;
            }
        } else
        {
            std::cout << "Wrong" << std::endl;
        }
    }
    return 0;
}

我认为你的程序有一个逻辑错误。如果一个单词包含超过10个不同的字符，会发生什么？如果小费是对的，不要计算。

您可以通过以下方式将字符添加到字符串中：

#include <iostream>
#include <string>
int main(){
    std::string str="123";
    str+='4';
    std::cout<<str<<std::endl;
    return 0;
}