C#井字棋开发中if条件符合却恒返回false问题排查

问题现象 #

• 基于C#开发井字棋游戏过程中，Updater类下的VerifyUserHasInputValidNumber(int userInput)方法设计目标为校验用户输入落子位置是否属于1-9的合法区间，合法输入返回true，非法输入返回false
• 实际运行时经调试打印确认传入的userInput参数值正确，但方法始终返回false，固定触发"Inputted an invalid position!"错误分支
• 已排除内存泄漏、语法格式错误类诱因

根因分析 #

该方法存在两处致命逻辑错误：

1. 逻辑运算符误用：判断数值是否落在闭区间内，需要同时满足「大于等于左边界」「小于等于右边界」两个条件，必须使用&&（逻辑与）运算符。原代码使用||（逻辑或）编写判断条件userInput >= 0 || userInput <= 10，该条件对所有整数恒成立——任意整数必然满足「大于等于0」或「小于等于10」两个条件中的至少一个，因此代码永远会进入if分支返回false。
2. 判断逻辑与边界值双重错误：即使将运算符修正为&&，原代码的边界值设置为0和10，会把非法值0、10判定为合法；同时if分支在条件满足时返回false，和「合法返回true」的设计目标完全相反。

修复方案 #

直接替换原有VerifyUserHasInputValidNumber方法即可，可删除调试用的打印语句：

public bool VerifyUserHasInputValidNumber(int userInput)
{
    // 输入值在1-9闭区间内即为合法
    return userInput >= 1 && userInput <= 9;
}

问题复现原代码 #

// 程序入口
Game newGame = new();
newGame.RunGame();


// 类定义
internal class Game
{
    private Player[] Players;
    private Updater GameUpdater;
    private Board GameBoard;

    public Game()
    {
        Players = new Player[2] { new(PlayerSymbol.X), new(PlayerSymbol.O) };
        GameUpdater = new();
        GameBoard = new();
    }

    public void RunGame()
    {
        while (true)
        {
            GameBoard.DisplayBoard();
            int currentPlayer = GameUpdater.SendPlayerTurnInfo();
            int playerInput = Players[currentPlayer].GetUserInput();
            bool playerInputtedValidNumber = GameUpdater.VerifyUserHasInputValidNumber(playerInput);

            if (playerInputtedValidNumber) 
            {
                bool playerInputtedUnusedNumber = GameUpdater.VerifyUserHasInputUnusedSpot(GameBoard.SendBoardPiecesData(--playerInput));

                if (playerInputtedUnusedNumber)
                {
                    PlayerSymbol currentPlayerSymbol = Players[currentPlayer].SendPlayerSymbol();
                    GameBoard.UpdateBoardPiecesData(playerInput, currentPlayerSymbol);
                }
                else
                {
                    Console.WriteLine("This position has already been used!");
                    continue;
                }
            }
            else
            {
                Console.WriteLine("Inputted an invalid position!");
                continue;
            }
        }
    }
}

internal class Board
{
    private string[]? BoardPieces;
    private string? BoardDisplay;

    public Board()
    {
        BoardPieces = new string[9] { " ", " ", " ", " ", " ", " ", " ", " ", " " };
        BoardDisplay = $" {BoardPieces[0]} | {BoardPieces[1]} | {BoardPieces[2]} \n---+---+---\n {BoardPieces[3]} | {BoardPieces[4]} | {BoardPieces[5]} \n---+---+---\n {BoardPieces[6]} | {BoardPieces[7]} | {BoardPieces[8]} ";
    }

    public void DisplayBoard()
    {
        Console.WriteLine(BoardDisplay);
    }

    public string SendBoardPiecesData(int userInput)
    {
        return BoardPieces[userInput];
    }

    public void UpdateBoardPiecesData(int userInput, PlayerSymbol playerSymbol)
    {
        BoardPieces[userInput] = $"{playerSymbol}";
        BoardDisplay = $" {BoardPieces[0]} | {BoardPieces[1]} | {BoardPieces[2]} \n---+---+---\n {BoardPieces[3]} | {BoardPieces[4]} | {BoardPieces[5]} \n---+---+---\n {BoardPieces[6]} | {BoardPieces[7]} | {BoardPieces[8]} ";
    }
 }

internal class Updater
{
    private int PlayerIndicator;

    public Updater()
    {
        PlayerIndicator = 1;
    }

    public int SendPlayerTurnInfo()
    {
        if (PlayerIndicator == 1)
        {
            PlayerIndicator = 0;
            return PlayerIndicator;
        } else
        {
            PlayerIndicator = 1;
            return PlayerIndicator;
        }
    }

    // 存在bug的原校验方法
    public bool VerifyUserHasInputValidNumber(int userInput)
    {
        Console.WriteLine(userInput);
        if (userInput >= 0 || userInput <= 10)
        {
            return false;
        } else
        {
            return true;
        }
    }

    public bool VerifyUserHasInputUnusedSpot(string userInput)
    {
        if (userInput == "X" || userInput == "O") return false;
        else return true;
    }
}

internal class Player
{
    private PlayerSymbol PlayerSymbol;

    public Player(PlayerSymbol playerSymbol)
    {
        PlayerSymbol = playerSymbol;
    }

    public int GetUserInput()
    {
        Console.Write($"It is currently {PlayerSymbol}'s turn. Which position would you like to play at? ");
        string? input = Console.ReadLine();
        bool isNumerical = int.TryParse(input, out int _);

        while (!isNumerical)
        {
            Console.Write("Invalid input, please input a number. ");
            input = Console.ReadLine();
            isNumerical = int.TryParse(input, out int _);
        }

        return int.Parse(input);
    }

    public PlayerSymbol SendPlayerSymbol()
    {
        return PlayerSymbol;
    }
}


// 枚举定义
enum PlayerSymbol
{
    X,
    O
}

内容的提问来源于stack exchange，提问作者Om Khadka