TicTacToe.java

import java.util.Scanner;

public class TicTacToe {

    static Scanner scan = new Scanner(System.in);
    public static void main(String[] args) {
        
            System.out.println("\nLet's play tic tac toe");

            //Create an array with three rows of '_' characters.
            char[][] board = {
                {'_', '_', '_'},
                {'_', '_', '_'},
                {'_', '_', '_'}
            };
            //Call the function printArray();
            printBoard(board);

             
              /*
              {Loop through turns.

                  if (X) turn {
                     Task 4: call askUser(). 
                     Task 5: populate the board using askUser's return value.
                  } else {
                      Task 4: call askUser(). 
                      Task 5: populate the board using askUser's return value. Then, print it.

                  }

               Call the function.
                   if return value == 3 {
                     print: X wins and break the loop
                  } else if return value == -3 {
                     print: O wins and break the loop
                  }

              } 
              */
            for (int i = 0; i < 9; i++) {

                if (i % 2 == 0) {
                    System.out.println("Turn: X");
                    int[] spot = askUser(board);
                    board[spot[0]][spot[1]] = 'X';
                    printBoard(board);

                } else {
                    System.out.println("Turn: O");
                    int[] spot = askUser(board);
                    board[spot[0]][spot[1]] = 'O';
                    printBoard(board);
                }

                if (checkWin(board) == 3) {
                    System.out.println("X wins!!");
                    break;
                } else if (checkWin(board) == -3) {
                    System.out.println("O wins!!");
                    break;
                } else if (i == 8) {
                    System.out.println("It's a tie!");
                }
    
            }

            scan.close();
        }


    /** Write a function that prints the board.
     * Function name - printBoard()
     * @param board (char[][])
     * 
     * Inside the function:
     *   1. print a new line.
     *   2. print the board.
     *      • separate each row by two lines. 
     *      • each row precedes a tab of space
     *      • each character in the grid has one space from the other character
     */        
    public static void printBoard(char[][] board) {
        System.out.print("\n");
        for (int i = 0; i < board.length; i++) {
            System.out.print("\t");
            for (int j = 0; j < board[i].length; j++) {
                System.out.print(board[i][j]+ " ");
            }
            System.out.print("\n\n");
        }
    }

   /**Write a function that lets the user choose a spot
     * Function name – askUser
     * @param board (char[][] board)
     * @return spot (int[])
     * 
     * Inside the function
     *   1. Asks the user: • pick a row and column number: 
     *   2. Check if the spot is taken. If so, let the user choose again.
     *   3. Return the row and column in an int[] array.
     * 
     */
    public static int[] askUser(char[][] board) {   
        System.out.print(" - pick a row and column number: ");

        int row = scan.nextInt();
        int column = scan.nextInt();

        while (board[row][column] != ('_')){
            System.out.print("Spot taken, try again: ");
            row = scan.nextInt();
            column = scan.nextInt();
        }
        
        int[] spot = {row, column};
        return spot; 
    }

    /** Write a function that determines the winner
     * Function name - checkWin 
     * @param board (char[][])
     * @return count (int)
     * 
     * Inside the function:
     *   1. Make a count variable that starts at 0.
     *   2. Check every row for a straight X or straight O (Task 7).
     *   3. Check every column for a straight X or straight O (Task 8).
     *   4. Check the left diagonal for a straight X or straight O (Task 9).
     *   5. Check the right diagonal for a straight X or straight O (Task 10).
     */
    public static int checkWin(char[][] board) {
        
        //Check each of 3 rows
        int count = 0;

        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
                if (board[i][j] == 'X') {
                    count++; //count each X as +1
                } else if (board[i][j] == 'O') { 
                    count--; //count each O as -1. 
                }
            }
            if (count == 3 || count == -3) {
                return count;
            } else {
                count = 0;
            }

        }

        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {

                if (board[j][i] == 'X') {
                    count++; //count each X as +1
                } else if (board[j][i] == 'O') { 
                    count--; //count each O as -1. 
                }
            }
            if (count == 3 || count == -3) {
                return count;
            } else {
                count = 0;
            }
        }

        for (int i = 0; i < 3; i++) {
            if (board[i][i] == 'X') {
                count++; //count each X as +1
            } else if (board[i][i] == 'O') { 
                count--; //count each O as -1. 
            }
        }

        if (count == 3 || count == -3) {
            return count;
        } else {
            count = 0;
        }

        for (int i = 0; i < 3; i++) {
            if (board[i][2-i] == 'X') {
                count++; //count each X as +1
            } else if (board[i][2-i] == 'O') { 
                count--; //count each O as -1. 
            }
        }

        return count;
    }

}