C++ Tic Tac toe game not showing X character - c++

Question

Novice programmer here. Trying to make a tic tac toe game. Everything so far works, except the character X doesn't appear. In the for loop is where I believe I have a problem but I cant seem to find anything wrong. Please help, any criticism is greatly appreciated. Good and bad. Thanks.
void playgame() {
std::string input;
while (true) {
std::cout << "Go player one" << std::endl;
getline (std::cin, input);
if (input != " ") {
char entered = input.c_str ()[0];
if (entered >= '1' && entered <= '9') {
int entered_num = entered - 0;
int index = entered_num - 1;
int row = index / 3;
int col = index % 3;
char grid_position = map[row][col];
if (grid_position == 'X' || grid_position == 'O') {
std::cout << "Space taken. Try again" << std::endl;
} else {
map[row][col] = (char) 'X';
break;
}
} else {
std::cout << "Only numbers 1 - 9" << std::endl;
}
} else {
std::cout << "Have to enter something, try again" << std::endl;
}
}
}
void generateGrid() {
int number = 1;
for (int x = 0; x < GRID_SIZE; x++) {
for (int y = 0; y < GRID_SIZE; y++) {
map[x][y] = std::to_string (number).c_str ()[0];
number += 1;
}
}
}
void tictacToeMap() {
std::cout << std::endl;
for (int x = 0; x < GRID_SIZE; x++) {
for (int y = 0; y < GRID_SIZE; y++) {
std::printf (" %c ", map[x][y]);
}
std::cout << std::endl;
}
}
TicTacToe() {
generateGrid ();
while (true) {
tictacToeMap ();
playgame ();
}
}
};
int main() {
TicTacToe tic;
return 0;
}

Answer 1

int entered_num = entered - 0;
Should be:
int entered_num = entered - '0';
To convert a '1' into a 1, you need to subtract '0' (the character we use to represent the digit zero), not 0 (the number zero). Subtracting zero doesn't do anything.