Tic-Tac-Toe Rust

fn get_piece(piece: i32) -> String
{
	let mut string = String::new();
	match piece
	{
		-1 => string.push_str(" "),
		0 => string.push_str("O"),
		1 => string.push_str("X"),
		_ => panic!("Invalid piece"),
	};
	return string;
}

struct GameState
{
	board: [i32; 9],
	curr_player: i32,
}

impl GameState
{
	fn new() -> GameState
	{
		GameState
		{
			board: [-1, -1, -1,
			        -1, -1, -1,
			        -1, -1, -1],
			curr_player: 0
		}
	}

	fn print(&self)
	{
		println!("");
		println!("Board:");
		println!(" {} | {} | {}       (0, 1, 2)", get_piece(self.board[0]), get_piece(self.board[1]), get_piece(self.board[2]));
		println!("-----------");
		println!(" {} | {} | {}       (3, 4, 5)", get_piece(self.board[3]), get_piece(self.board[4]), get_piece(self.board[5]));
		println!("-----------");
		println!(" {} | {} | {}       (6, 7, 8)", get_piece(self.board[6]), get_piece(self.board[7]), get_piece(self.board[8]));
	}

	fn place_piece(&mut self, slot: i32) -> bool
	{
		if self.board[slot as usize] == -1
		{
			self.board[slot as usize] = self.curr_player;
			self.curr_player = 1 - self.curr_player;
			return true;
		}
		return false;
	}

	fn winning_player(&self) -> i32
	{
		// Fuck for loops.
		if self.board[0] == self.board[1] && self.board[1] == self.board[2]
		{
			return self.board[0];
		}
		else if self.board[3] == self.board[4] && self.board[4] == self.board[5]
		{
			return self.board[3];
		}
		else if self.board[6] == self.board[7] && self.board[7] == self.board[8]
		{
			return self.board[6];
		}
		else if self.board[0] == self.board[3] && self.board[3] == self.board[6]
		{
			return self.board[0];
		}
		else if self.board[1] == self.board[4] && self.board[4] == self.board[7]
		{
			return self.board[1];
		}
		else if self.board[2] == self.board[5] && self.board[5] == self.board[8]
		{
			return self.board[2];
		}
		else if self.board[0] == self.board[4] && self.board[4] == self.board[8]
		{
			return self.board[0];
		}
		else if self.board[2] == self.board[4] && self.board[4] == self.board[6]
		{
			return self.board[2];
		}
		return -1;
	}
}

fn get_input_num() -> i32
{
	let stdin = std::io::stdin();

	loop
	{
		println!("Enter slot number:");

		let mut user_input = String::new();

		match stdin.read_line(&mut user_input)
		{
			Err(error) => panic!("Failure reading line: {}", error),
			_ => {}
		}

		if user_input.len() < 2
		{
			println!("Invalid slot number. Try again.");
			continue;
		}

		let trimmed_length = user_input.len()-2;
		let trimmed_user_input = &user_input[..trimmed_length];

		let number = match trimmed_user_input.parse::<i32>()
		{
			Ok(n) => n,
			Err(error) => { println!("{}. Try again.", error); continue; }
		};

		if number < 0 || number >= 9
		{
			println!("Number out of range. Try again.");
			continue;
		}

		return number;
	}
}

fn main()
{
	let mut game_state = GameState::new();

	loop
	{
		game_state.print();
		let slot_number = get_input_num();
		println!("You chose {}", slot_number);

		if !game_state.place_piece(slot_number)
		{
			println!("Invalid slot. Try again.");
		}

		let winner = game_state.winning_player();
		if winner != -1
		{
			game_state.print();
			println!("Player {} wins!", winner);
			break;
		}
	}	
}