Why am I getting the error "no match for 'operator==' " when comparing strings? [closed]

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For every line where I compare a string to another string, I keep getting the error:

No match for 'operator=='

Code:

#include <iostream>
#include <conio.h>
#include <string>
#include <curses.h>
using namespace std;

int word_number, state, i, x, n;
bool correct[25], playing = true, set_complete, valid, match;
string word, word_list[25], head, upper, body, lower, blanks, input, guessed, alphabet = "abcdefghijklmnopqrstuvwxyz";
size_t found;

void play(), initialize(), print(), validate(), progress();

int main()
{
    initscr();
    while (playing)
    {
        play();
        printw("Would you like to continue playing?");
        input = getch();
        if (input == "n"||input == "N")
        {
            playing = false;
        }
    }
    endwin();
}

void initialize()
{
    if (word_number != 0)
    {
        word_number++;
    }

    if (word_number == 25)
    {
        set_complete = true;
    }
    state = 0;
    head = "";
    upper = "";
    body = "";
    lower = "";
    blanks = "";
    guessed = "";
    word  =  word_list[word_number];
    for (i = 0; i<strlen(word.c_str()); i++)
    {
        blanks += "_";
    }
}

void play()
{
    initialize();
    while(!set_complete)
    {
        start:
        input = getch();
        validate();

    }
}

void validate()
{

    for (i = 0, valid = false; i <= 25; i++)
    {
        if (input == alphabet[i])
        {
            valid = true;
        }
    }

    if (!valid)
    {
        goto start;
    }

    for (i = 0, match = false; i<strlen(guessed.c_str()); i++)
    {
        if (guessed[i] == input)
        {
            match = true;
        }
    }

    if (!match)
    {
        guessed += input;
    }

    for (i = 0, match = false; i<strlen(word.c_str()); i++)
    {
        if (input == word[i])
        {
            blanks[i] = input;
            match = true;
        }
    }

    if (!match)
    {
        state++;
    }
    else
    {
        x++;
    }

    if (x == strlen(word.c_str()))
    {
        correct[word_number] = 1;
        initialize();
    }
}

void print()
{
    switch (state)
    {
        case 1:
        head = "(Q)";
        break;
        case 2:
        upper = " |";
        break;
        case 3:
        upper = "\|";
        break;
        case 4:
        upper = "\|/";
        break;
        case 5:
        body = "|";
        break;
        case 6:
        lower = "/ ";
        break;
        case 7:
        lower = "/ \\";
        break;
        default:
        break;
    }

    printw("   ______\n");
    printw("  /      \\\开发者_开发技巧n");
    printw("  |     %s\n", head.c_str());
    printw("  |    %s\n", upper.c_str());
    printw("  |     %s\n", body.c_str());
    printw("  |    %s\n", lower.c_str());
    printw("__|__\n");
    if (!valid)
    {
        printw("Only lowercase letters are allowed!\n");
        valid = true;
    }
    printw("%s\n", guessed.c_str());
    for (i = 0; i<strlen(word.c_str()); i++)
    {
        printw("%s ", blanks[i].c_str());
    }
    refresh();
}

void progress()
{
    for (i = 0; i<25; i++)
    {
        if (correct[i] =  = 1)
        {
            printw("%s -- Correct!\n", word_list[word_number].c_str());
        }
        else
        {
            printw("%s -- Incorrect.\n", word_list[word_number].c_str());
        }
    }
}

Here is my source code in its entirety

The errors occur on lines 72, 85, and 98

EDIT: After removing the labels, as suggested, the solution to my problem was simply to replace the comparison instances of input to a char with input[0] to a char.

---

if (input == alphabet[i]) has a std::string on its left and a char on its right, so the comparison is obviously not defined.

You perhaps wanted to iterate through all characters in input and compare input[n] (n being the current index) if it is contained in alphabet. You can use alphabet.find to get this much quicker (or you can exploit the ASCII representation of the characters).

---

In each of these lines you enumerated you compare a std::string with a char.

In line 72, for example, are you checking if input has a character outside of alphabet? If so, and assuming the alphabet is sorted, try

std::set<char> ins(in.begin(), in.end());
if( *ins.begin() < *alph.begin() || *ins.rbegin() > *alph.rbegin() )
    valid = false;

where in is input and alph is alphabet.