c# - C# use of unassigned variable?

Question

So basically I have a class for a TicTacToe game and a derived class just to practice using inheritance. The class has several methods and all should work perfectly fine but in the main function, when I finally make three objects of the derived class I get three errors "use of unassigned local variable 'boardOne'" "use of unassigned local variable 'boardTwo'" and "use of unassigned local variable 'boardThree'". I do not understand why this is, they are objects, not variables.

    public class TicTacToe
    {
        protected char[] boardCells = new char[9];
        public int boardSpacesUsed;
        public TicTacToe()                            //constructor
        {
            boardCells[0] = '1';
            boardCells[1] = '2';
            boardCells[2] = '3';
            boardCells[3] = '4';
            boardCells[4] = '5';
            boardCells[5] = '6';
            boardCells[6] = '7';
            boardCells[7] = '8';
            boardCells[8] = '9';
            boardCells[9] = '\0';
            int boardSpacesUsed = 0;
        }
        public void playerOneMove()
        {
            bool space = false;
            char cell = '\0';
            while (space == false)
            {
                Console.WriteLine("Please enter cell number you wish to mark: ");
                cell = Convert.ToChar(Console.ReadLine());
                switch (cell)
                {
                    case '1':
                        if (boardCells[0] == 'X' || boardCells[0] == 'O')
                        {
                            Console.WriteLine("Illegal Move");
                        }
                        else
                        {
                            boardCells[0] = 'X';
                            space = true;
                        }
                        break;
                    case '2':
                        if (boardCells[1] == 'X' || boardCells[1] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[1] = 'X';
                            space = true;
                        }
                        break;
                    case '3':
                        if (boardCells[2] == 'X' || boardCells[2] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[2] = 'X';
                            space = true;
                        }
                        break;
                    case '4':
                        if (boardCells[3] == 'X' || boardCells[3] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[3] = 'X';
                            space = true;
                        }
                        break;
                    case '5':
                        if (boardCells[4] == 'X' || boardCells[4] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[4] = 'X';
                            space = true;
                        }
                        break;
                    case '6':
                        if (boardCells[5] == 'X' || boardCells[5] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[5] = 'X';
                            space = true;
                        }
                        break;
                    case '7':
                        if (boardCells[6] == 'X' || boardCells[6] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[6] = 'X';
                            space = true;
                        }
                        break;
                    case '8':
                        if (boardCells[7] == 'X' || boardCells[7] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[7] = 'X';
                            space = true;
                        }
                        break;
                    case '9':
                        if (boardCells[8] == 'X' || boardCells[8] == 'O')
                            Console.WriteLine("Illegal Move");
                        else
                        {
                            boardCells[8] = 'X';
                            space = true;
                        }
                        break;
                    default:
                        Console.WriteLine("Cell Does NOT Exist!");
                        break;
                }// end of switch statement
            }//end of while loop
            boardSpacesUsed++;
        }// end of playerOneMove();
        public void CPUMove()                                                   //method marks cell for CPU
        {
            int iCell = 0;
            bool space = false;
            while (space == false)
            {
                Random rand = new Random();
                iCell = rand.Next(1, 9);
                switch (iCell)                                              //switch statement to mark the cell
                {
                    case 1:
                        if (boardCells[0] == 'X' || boardCells[0] == 'O')
                        {
                            space = false;
                        }
                        else
                        {
                            boardCells[0] = 'O';
                            space = true;
                        }
                        break;
                    case 2:
                        if (boardCells[1] == 'X' || boardCells[1] == 'O')
                            space = false;
                        else
                        {
                            boardCells[1] = 'O';
                            space = true;
                        }
                        break;
                    case 3:
                        if (boardCells[2] == 'X' || boardCells[2] == 'O')
                            space = false;
                        else
                        {
                            boardCells[2] = 'O';
                            space = true;
                        }
                        break;
                    case 4:
                        if (boardCells[3] == 'X' || boardCells[3] == 'O')
                            space = false;
                        else
                        {
                            boardCells[3] = 'O';
                            space = true;
                        }
                        break;
                    case 5:
                        if (boardCells[4] == 'X' || boardCells[4] == 'O')
                            space = false;
                        else
                        {
                            boardCells[4] = 'O';
                            space = true;
                        }
                        break;
                    case 6:
                        if (boardCells[5] == 'X' || boardCells[5] == 'O')
                            space = false;
                        else
                        {
                            boardCells[5] = 'O';
                            space = true;
                        }
                        break;
                    case 7:
                        if (boardCells[6] == 'X' || boardCells[6] == 'O')
                            space = false;
                        else
                        {
                            boardCells[6] = 'O';
                            space = true;
                        }
                        break;
                    case 8:
                        if (boardCells[7] == 'X' || boardCells[7] == 'O')
                            space = false;
                        else
                        {
                            boardCells[7] = 'O';
                            space = true;
                        }
                        break;
                    case 9:
                        if (boardCells[8] == 'X' || boardCells[8] == 'O')
                            space = false;
                        else
                        {
                            boardCells[8] = 'O';
                            space = true;
                        }
                        break;
                }
            }
            boardSpacesUsed++;
        }
        public void getBoardCells()
        {
            Console.WriteLine("  " + " " + "  |  " + " " + "  |  " + " ");
            Console.WriteLine("  " + boardCells[0] + "  |  " + boardCells[1] + "  |  " + boardCells[2]);
            Console.WriteLine("__" + "_" + "__|__" + "_" + "__|__" + "_");
            Console.WriteLine("  " + " " + "  |  " + " " + "  |  " + " ");
            Console.WriteLine("  " + boardCells[3] + "  |  " + boardCells[4] + "  |  " + boardCells[5]);
            Console.WriteLine("__" + "_" + "__|__" + "_" + "__|__" + "_");
            Console.WriteLine("  " + " " + "  |  " + " " + "  |  " + " ");
            Console.WriteLine("  " + boardCells[6] + "  |  " + boardCells[7] + "  |  " + boardCells[8]);
            Console.WriteLine("  " + " " + "  |  " + " " + "  |  " + " ");
        }
        public bool playerOneWinCheck(ref int score)
        {
            bool check = false;
            if (boardCells[0] == 'X' && boardCells[1] == 'X' && boardCells[2] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[3] == 'X' && boardCells[4] == 'X' && boardCells[5] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[6] == 'X' && boardCells[7] == 'X' && boardCells[8] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[0] == 'X' && boardCells[3] == 'X' && boardCells[6] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[1] == 'X' && boardCells[4] == 'X' && boardCells[7] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[2] == 'X' && boardCells[5] == 'X' && boardCells[8] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[0] == 'X' && boardCells[4] == 'X' && boardCells[8] == 'X')
            {
                check = true;
                score++;
            }
            if (boardCells[6] == 'X' && boardCells[4] == 'X' && boardCells[2] == 'X')
            {
                check = true;
                score++;
            }
            if (check == true)
                return true;
            else
                return false;
        }
        public bool CPUWinCheck(ref int score)                                                          //Method to check to see if CPU won INCRAMENTS SCORE UP ONE IF ANYTHING HOLDS TRUE
        {
            bool check = false;
            if (boardCells[0] == 'O' && boardCells[1] == 'O' && boardCells[2] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[3] == 'O' && boardCells[4] == 'O' && boardCells[5] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[6] == 'O' && boardCells[7] == 'O' && boardCells[8] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[0] == 'O' && boardCells[3] == 'O' && boardCells[6] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[1] == 'O' && boardCells[4] == 'O' && boardCells[7] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[2] == 'O' && boardCells[5] == 'O' && boardCells[8] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[0] == 'O' && boardCells[4] == 'O' && boardCells[8] == 'O')
            {
                check = true;
                score++;
            }
            if (boardCells[6] == 'O' && boardCells[4] == 'O' && boardCells[2] == 'O')
            {
                check = true;
                score++;
            }
            if (check == true)
                return true;
            else
                return false;
        }
        ~TicTacToe()
        {
            for (int c = 0; c <= 10; c++)
            {
                boardCells[c] = '\0';

            }
            boardSpacesUsed = 0;
        }
    }
    public class ThreeD : TicTacToe
    {

        public void threeDWinCheck(ThreeD boardOne, ThreeD boardTwo, ThreeD boardThree, ref int score) //new function to check to see ThreeD wins
        {
            if (boardOne.boardCells[0] == 'X' && boardTwo.boardCells[0] == 'X' && boardThree.boardCells[0] == 'X')
            {
                score++;
                Console.WriteLine("did it make it");
            }
            if (boardOne.boardCells[1] == 'X' && boardTwo.boardCells[1] == 'X' && boardThree.boardCells[1] == 'X')
                score++;
            if (boardOne.boardCells[2] == 'X' && boardTwo.boardCells[2] == 'X' && boardThree.boardCells[2] == 'X')
                score++;
            if (boardOne.boardCells[3] == 'X' && boardTwo.boardCells[3] == 'X' && boardThree.boardCells[3] == 'X')
                score++;
            if (boardOne.boardCells[4] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[4] == 'X')
                score++;
            if (boardOne.boardCells[5] == 'X' && boardTwo.boardCells[5] == 'X' && boardThree.boardCells[5] == 'X')
                score++;
            if (boardOne.boardCells[6] == 'X' && boardTwo.boardCells[6] == 'X' && boardThree.boardCells[6] == 'X')
                score++;
            if (boardOne.boardCells[7] == 'X' && boardTwo.boardCells[7] == 'X' && boardThree.boardCells[7] == 'X')
                score++;
            if (boardOne.boardCells[8] == 'X' && boardTwo.boardCells[8] == 'X' && boardThree.boardCells[8] == 'X')
                score++;
            if (boardOne.boardCells[0] == 'X' && boardTwo.boardCells[1] == 'X' && boardThree.boardCells[2] == 'X')
                score++;
            if (boardOne.boardCells[2] == 'X' && boardTwo.boardCells[1] == 'X' && boardThree.boardCells[0] == 'X')
                score++;
            if (boardOne.boardCells[3] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[5] == 'X')
                score++;
            if (boardOne.boardCells[5] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[3] == 'X')
                score++;
            if (boardOne.boardCells[6] == 'X' && boardTwo.boardCells[7] == 'X' && boardThree.boardCells[8] == 'X')
                score++;
            if (boardOne.boardCells[8] == 'X' && boardTwo.boardCells[7] == 'X' && boardThree.boardCells[6] == 'X')
                score++;
            if (boardOne.boardCells[0] == 'X' && boardTwo.boardCells[3] == 'X' && boardThree.boardCells[6] == 'X')
                score++;
            if (boardOne.boardCells[6] == 'X' && boardTwo.boardCells[3] == 'X' && boardThree.boardCells[0] == 'X')
                score++;
            if (boardOne.boardCells[1] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[7] == 'X')
                score++;
            if (boardOne.boardCells[7] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[1] == 'X')
                score++;
            if (boardOne.boardCells[2] == 'X' && boardTwo.boardCells[5] == 'X' && boardThree.boardCells[8] == 'X')
                score++;
            if (boardOne.boardCells[8] == 'X' && boardTwo.boardCells[5] == 'X' && boardThree.boardCells[2] == 'X')
                score++;
            if (boardOne.boardCells[0] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[8] == 'X')
                score++;
            if (boardOne.boardCells[8] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[0] == 'X')
                score++;
            if (boardOne.boardCells[2] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[6] == 'X')
                score++;
            if (boardOne.boardCells[6] == 'X' && boardTwo.boardCells[4] == 'X' && boardThree.boardCells[2] == 'X')
                score++;

        }
        public void CPUThreeDWinCheck(ThreeD boardOne, ThreeD boardTwo, ThreeD boardThree, ref int score)           //new function to check CPU ThreeD wins
        {
            if (boardOne.boardCells[0] == 'O' && boardTwo.boardCells[0] == 'O' && boardThree.boardCells[0] == 'O')
                score++;
            if (boardOne.boardCells[1] == 'O' && boardTwo.boardCells[1] == 'O' && boardThree.boardCells[1] == 'O')
                score++;
            if (boardOne.boardCells[2] == 'O' && boardTwo.boardCells[2] == 'O' && boardThree.boardCells[2] == 'O')
                score++;
            if (boardOne.boardCells[3] == 'O' && boardTwo.boardCells[3] == 'O' && boardThree.boardCells[3] == 'O')
                score++;
            if (boardOne.boardCells[4] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[4] == 'O')
                score++;
            if (boardOne.boardCells[5] == 'O' && boardTwo.boardCells[5] == 'O' && boardThree.boardCells[5] == 'O')
                score++;
            if (boardOne.boardCells[6] == 'O' && boardTwo.boardCells[6] == 'O' && boardThree.boardCells[6] == 'O')
                score++;
            if (boardOne.boardCells[7] == 'O' && boardTwo.boardCells[7] == 'O' && boardThree.boardCells[7] == 'O')
                score++;
            if (boardOne.boardCells[8] == 'O' && boardTwo.boardCells[8] == 'O' && boardThree.boardCells[8] == 'O')
                score++;
            if (boardOne.boardCells[0] == 'O' && boardTwo.boardCells[1] == 'O' && boardThree.boardCells[2] == 'O')
                score++;
            if (boardOne.boardCells[2] == 'O' && boardTwo.boardCells[1] == 'O' && boardThree.boardCells[0] == 'O')
                score++;
            if (boardOne.boardCells[3] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[5] == 'O')
                score++;
            if (boardOne.boardCells[5] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[3] == 'O')
                score++;
            if (boardOne.boardCells[6] == 'O' && boardTwo.boardCells[7] == 'O' && boardThree.boardCells[8] == 'O')
                score++;
            if (boardOne.boardCells[8] == 'O' && boardTwo.boardCells[7] == 'O' && boardThree.boardCells[6] == 'O')
                score++;
            if (boardOne.boardCells[0] == 'O' && boardTwo.boardCells[3] == 'O' && boardThree.boardCells[6] == 'O')
                score++;
            if (boardOne.boardCells[6] == 'O' && boardTwo.boardCells[3] == 'O' && boardThree.boardCells[0] == 'O')
                score++;
            if (boardOne.boardCells[1] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[7] == 'O')
                score++;
            if (boardOne.boardCells[7] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[1] == 'O')
                score++;
            if (boardOne.boardCells[2] == 'O' && boardTwo.boardCells[5] == 'O' && boardThree.boardCells[8] == 'O')
                score++;
            if (boardOne.boardCells[8] == 'O' && boardTwo.boardCells[5] == 'O' && boardThree.boardCells[2] == 'O')
                score++;
            if (boardOne.boardCells[0] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[8] == 'O')
                score++;
            if (boardOne.boardCells[8] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[0] == 'O')
                score++;
            if (boardOne.boardCells[2] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[6] == 'O')
                score++;
            if (boardOne.boardCells[6] == 'O' && boardTwo.boardCells[4] == 'O' && boardThree.boardCells[2] == 'O')
                score++;

        }

        ~ThreeD()
        {
            for (int c = 0; c < 10; c++)
            {
                boardCells[c] = '\0';
            }


        }

    }

    static void Main(string[] args)
    {
        ThreeD boardOne;                                                                        //1st of three objects for first board
        ThreeD boardTwo;                                                                        //2nd
        ThreeD boardThree;                                                                      //3rd
        int boardSelection = 0;                                                                     //picks witch object to mark in 
        int counter = 0;                                                                        //counter for while loop
        int playerOneScore = 0;                                                                 //score for user
        int CPUScore = 0;                                                                       //score for cpu
        int CPUBoardSelection = 0;
        Random rand = new Random();
        int randomNum = rand.Next(1, 2);

        if (randomNum == 1)                                                                     // if randomNum = 1, user goes first
        {
            Console.WriteLine("You first");
            while (true)
            {
                boardOne.getBoardCells();                                               
                boardTwo.getBoardCells();
                boardThree.getBoardCells();

                Console.WriteLine("Choose which board you wish to mark in. (1 - 3)");       //promts you to pick board
                bool board = false;

Answer 1

首先，boardOne和boardTwo是boardThree变量，在这种情况下是方法范围内的局部变量Main()。像任何其他变量一样，它们需要有效的数据类型，在您的情况下，类型是ThreeD类。但仅此一项并不能使它们成为对象，仅定义它们的数据类型。

只有当您使用此类创建新实例（内存中的新单个对象）时，变量才会成为对象。所以它们必须被初始化：

ThreeD boardOne = new ThreeD();
ThreeD boardTwo = new ThreeD();
ThreeD boardThree = new ThreeD();

这样，当getBoardCells()调用该方法时，每个变量都指向它们所代表的内存中的对象，该对象包含该方法。null如果没有赋值，变量默认是相等的。当然，由于null没有一种方法getBoardCells()，你得到的编译器错误是有意义的。

Answer 2

是的，编译器是对的：您正在尝试使用未分配的变量：

static void Main(string[] args)
{
    // It's just a declaration; no value assigned to boardOne; boardOne contains trash
    ThreeD boardOne;                                                                        
    // It's just a declaration; no value assigned to boardTwo; boardTwo contains trash 
    ThreeD boardTwo;                                                                  
    // It's just a declaration; no value assigned to boardThree; boardThree contains trash
    ThreeD boardThree;                                                                      
    ....   
    if (randomNum == 1)                                                                     
    {
        Console.WriteLine("You first");
        while (true)
        {
            boardOne.getBoardCells(); // <- And here you're trying to access the trash   

它应该是这样的：

static void Main(string[] args)
{
    // boardOne is declared and assigned
    ThreeD boardOne = new ThreeD();                                                                         
    // boardTwo is declared and assigned
    ThreeD boardTwo = new ThreeD();                                                                  
    // boardThree is declared and assigned
    ThreeD boardThree = new ThreeD();                                                                      
    ....   
    if (randomNum == 1)                                                                     
    {
        Console.WriteLine("You first");
        while (true)
        {
            boardOne.getBoardCells(); // <- Quite OK   

Answer 3

您缺少的创建对象实例

ThreeD boardOne = new ThreeD();

ThreeD boardTwo = new ThreeD();

ThreeD boardThree = new ThreeD();

Answer 4

为了使用局部变量，你必须初始化它：

var boardOne = new ThreeD();
var boardTwo = new ThreeD();
...

Answer 5

您需要实例化该类：

ThreeD boardOne = new ThreeD();
ThreeD boardTwo = new ThreeD();
ThreeD boardThree = new ThreeD();

如果您不这样做，您将无法访问非静态类成员。

Answer 6

您必须初始化板对象，因为 C# 编译器不允许使用未初始化的变量。检查此链接：编译器错误 CS0165

static void Main(string[] args)
{
    ThreeD boardOne = new ThreeD();                                                                        //1st of three objects for first board
    ThreeD boardTwo = new ThreeD();                                                                        //2nd
    ThreeD boardThree = new ThreeD();    

   //..............
   // ..............
 }