error: invalid conversion from ‘char*’ to ‘char’ [-fpermissive]

Question

When I try and compile this I get the error shown above, and I don;t know how to fix this. I'm VERY new to C++ so please feel free to destroy everything, as I will learn from advice.

Input:

.............
.............
..XXX.....X..
..XXX.....X..
..XXX........
..XXX........
..XXXXXXX....
..XXXXXXX....
..XXXXXXX....
.............
.............

Output:

.............
.............
..OOO.....O..
..OOO.....O..
..OOO........
..OOO........
..OOOOOOO....
..OOOOOOO....
..OOOOOOO....
.............
.............

If i change it so that instead of

if (board[i][j] == older) {
   board[i][j] = newer; 

I do.

if (board[i][j] == "X") {
   board[i][j] = "0"; 

It works

#include <fstream>
#include <iostream>
#include <cstdlib> 
#include <vector>

int main(int argc, char* argv[]) {

    std::ifstream in_str(argv[1]);
    //Check that the file was properly opened      
    if (!in_str.good()) {
        std::cout << "Can't open " << argv[1] << " to read.\n";
        return (1);
    }
    std::string value;
    std::vector<std::string> board;

    while (in_str >> value) {
        board.push_back(value);
        }


    if (argv[3] == std::string ("replace")) {
        std::string older(argv[4]);
        std::string newer(argv[5]);
        for (unsigned int i = 0; i < board.size(); i++) {
            for (unsigned int j = 0; j < board[0].size(); j++) {
                if (board[i][j] == older) {
                    board[i][j] = newer;
                }
            }
        } 

Answer 1

Since board is defined as:

std::vector<std::string> board;

board[i][j] evaluates to a char& .

Since older and newer are defined to as:

    std::string older(argv[4]);
    std::string newer(argv[5]);

The following are wrong:

board[i][j] == older
board[i][j] = newer;

You can't compare a std::string with a char and you can't assign a std::string to a char .

The following are also wrong:

board[i][j] == "X"
board[i][j] = "O";

You can't compare a char const*/char*/char [2] with a char and you can't assign such an object to a char .

You can use:

board[i][j] == older
board[i][j] = newer;

if older and newer are of type char . I suggest changing the declaration of those variables to:

    char older = argv[4][0];
    char newer = argv[5][0];

Answer 2

any item in board matrix is char. and older and newer are string (char*) in if (board[i][j] == older) code you try to compare char * and char set older and newer to char instead of string

Answer 3

To fix this problem, You might compare with older[0] and newer[0] since they will return refrence to char which should work.

As others have pointed out, as of now your comparing a string object with a single char which is problematic. But older[0]/newer[0] will return reference to char.