A simple tic tac toe game

tic-tac-toe.cpp

#include <cstdlib>
#include <iostream>
using namespace std;

void board();
void player_choose(int player);
bool check_winner(int player);
void show_game(int player_winner);
char get_value(char mark);

char game_matrix[3][3] = {
	'1', '2', '3', 
	'4', '5', '6',
	'7', '8', '9'
};

int main() {
	int player = 1;
	int old_player;
	int turns = 1;
	
	do {
		board();
		player_choose(player);
		old_player = player;
		player = (player == 1)?2:1;
		turns++;
		if(turns == 10) {
			old_player = 0;
		}
	} while(!check_winner(old_player) && turns < 10);
	
	show_game(old_player);
	return 0;
}

void board() {
        system("clear");
	cout << "     |     |     " << endl;
	for(size_t r=0; r<3; r++) {
		cout << "  " << game_matrix[r][0] << "  |  " << game_matrix[r][1] << "  |  " << game_matrix[r][2] << endl;
		cout << "_____|_____|_____" << endl;
		cout << "     |     |     " << endl;
	}
}

void player_choose(int player) {
	char choose;
	char mark = (player == 1)?'X':'O';
	cout << "Inserisci " << mark << ": ";
	cin >> choose;

	for(size_t r=0; r<3; r++) {
		for(size_t c=0; c<3; c++) {
			if(game_matrix[r][c] == choose) {
				game_matrix[r][c] = mark;
			}
		}
	}
}


bool check_winner(int player) {
	bool winner = false;
	char mark = (player == 1)?'X':'O';

	for(size_t r=0; r<3; r++) {
		int count = 0;
                for(size_t c=0; c<3; c++) {
			if(game_matrix[r][c] == mark) {
				count++;
			}
		}
		
		if(count == 3) {
			winner = true;
			break;
		}
	}

	if(!winner) {
		for(size_t r=0; r<3; r++) {
			int count = 0;
                	for(size_t c=0; c<3; c++) {
                        	if(game_matrix[c][r] == mark) {
					count++;
                	        }
        	        }
	
	                if(count == 3) {
				winner = true;
                        	break;
                	}
        	}
	}

	if(!winner) {
		int count = 0;
		for(size_t i=0; i<3; i++) {
			if(game_matrix[i][i] == mark) {
                                count++;
		        }
			if(count == 3) {
				winner = true;
				break;
			}
		}
	}	

	if(!winner) {
                int count = 0;
                for(size_t c=2, r=0; c>0, r<3; c--, r++) {
                        if(game_matrix[r][c] == mark) {
                                count++;
                        }
                        if(count == 3) {
                                winner = true;
                                break;
                        }
                }
        }
	return winner;			
}

void show_game(int winner) {
	system("clear");

	if(winner == 0) {
                cout << "TIE!!!!" << endl;
        } else {
                cout << "Winner player " << winner << endl;
        }

        cout << "     |     |     " << endl;
        for(size_t r=0; r<3; r++) {
		char cell1 = get_value(game_matrix[r][0]);
		char cell2 = get_value(game_matrix[r][1]);
		char cell3 = get_value(game_matrix[r][2]);

                cout << "  " << cell1 << "  |  " << cell2 << "  |  " << cell3 << endl;
                cout << "_____|_____|_____" << endl;
                cout << "     |     |     " << endl;
        }
}

char get_value(char mark) {
	if(mark == 'X' || mark == 'O') {
		return mark;
	} else {
		return ' ';
	}
}