TicTacToe example implementation in Plain C

main.c

#include <raylib.h>
#include <stdint.h>

const uint8_t kEmptyPlayer = 0;

typedef struct Board {
  uint8_t positions[3][3];
} Board;

Board ConstructBoard() {
  Board board;

  for (uint8_t x = 0; x < 3; x += 1) {
	for (uint8_t y = 0; y < 3; y += 1) {
	  board.positions[x][y] = kEmptyPlayer;
	}
  }

  return board;
}

/**
 * Checks whether a given player has won.
 * @param board The current game board
 * @param player The player we want to check for
 * @return True if that player wins on this board
 */
bool CheckPlayerWins(Board board, uint8_t player) {
  for (uint8_t i = 0; i < 3; i += 1) {
	// horizontals
	if (board.positions[i][0] == player
		&& board.positions[i][1] == player
		&& board.positions[i][2] == player) {
	  return true;
	}

	// verticals
	if (board.positions[0][i] == player
		&& board.positions[1][i] == player
		&& board.positions[2][i] == player) {
	  return true;
	}
  }

  // diagonal
  if (board.positions[0][0] == player
	  && board.positions[1][1] == player
	  && board.positions[2][2] == player) {
	return true;
  }

  // diagonal
  if (board.positions[2][0] == player
	  && board.positions[1][1] == player
	  && board.positions[0][2] == player) {
	return true;
  }

  return false;
}

/**
 * @param board The current game board
 * @return True if the board is full (meaning no 0 values on it)
 */
bool BoardIsFull(Board board) {
  for (uint8_t x = 0; x < 3; x += 1) {
	for (uint8_t y = 0; y < 3; y += 1) {
	  if (board.positions[x][y] == kEmptyPlayer) {
		return false;
	  }
	}
  }

  return true;
}

void InitializeWindow() {
  const uint16_t kWindowWidth = 800;
  const uint16_t kWindowHeight = 600;

  InitWindow(kWindowWidth, kWindowHeight, "Tic-Tac-Toe");
  SetTargetFPS(60);
}

uint8_t NextPlayer(uint8_t current_player) {
  return current_player == 2 ? 1 : 2;
}

/**
 * Draws the square on the screen as well as its current value.
 * Will also check if the square has been clicked
 *
 * @return True if the square has been clicked and is active
 */
bool UpdateSquare(uint8_t x, uint8_t y, uint8_t current_value) {
  const uint16_t square_size = 60;
  const uint16_t offset_x = (GetScreenWidth() - square_size * 3) / 2;
  const uint16_t offset_y = (GetScreenHeight() - square_size * 3) / 2;

  uint16_t position_x = offset_x + x * square_size;
  uint16_t position_y = offset_y + y * square_size;

  DrawRectangleLines(position_x, position_y, square_size, square_size, BLACK);

  if (current_value == 1) {
	DrawText("x", position_x + 20, position_y + 10, square_size - 20, BLACK);
  } else if (current_value == 2) {
	DrawText("o", position_x + 20, position_y + 10, square_size - 20, BLACK);
  } else if (IsMouseButtonPressed(MOUSE_BUTTON_LEFT)) {
	Vector2 mouse_position = GetMousePosition();
	if (mouse_position.x > position_x
		&& mouse_position.x < position_x + square_size
		&& mouse_position.y > position_y
		&& mouse_position.y < position_y + square_size) {
	  return true;
	}
  }

  return false;
}

/**
 * Draws the board and if a square has been clicked
 * the value will be updated for that square and the players will be switched.
 */
void UpdateBoard(Board *board, uint8_t *current_player) {
  for (uint8_t x = 0; x < 3; x += 1) {
	for (uint8_t y = 0; y < 3; y += 1) {
	  if (UpdateSquare(x, y, board->positions[x][y])) {
		board->positions[x][y] = *current_player;
		*current_player = NextPlayer(*current_player);
	  }
	}
  }
}

void Run() {
  uint8_t current_player = NextPlayer(0);
  Board board = ConstructBoard();
  char *won_message = "";

  while (!WindowShouldClose()) {
	BeginDrawing();
	ClearBackground(RAYWHITE);

	UpdateBoard(&board, &current_player);

	if (CheckPlayerWins(board, 1)) {
	  board = ConstructBoard();
	  won_message = "Player 'x' won!";
	}

	if (CheckPlayerWins(board, 2)) {
	  board = ConstructBoard();
	  won_message = "Player 'o' won!";
	}

	if (BoardIsFull(board)) {
	  board = ConstructBoard();
	  won_message = "Game was a draw!";
	}

	DrawText(TextFormat("Current Player %c", current_player == 1 ? 'x' : 'o'), 25, 10, 40, BLACK);
	DrawText(won_message, 25, 60, 40, BLACK);

	EndDrawing();
  }
}

int main() {
  InitializeWindow();
  Run();
  CloseWindow();
  return 0;
}