c++ - 石头，布，剪刀，奇数输出

Question

对于我的类(class)项目，我们要制作一个“石头剪刀布”游戏，使用一个函数来显示菜单和验证输入，以及一个函数来确定谁赢了。当我绕过第一个函数时，我的代码将编译并正常运行。但是，当我同时使用这两个函数并输入 1、2 或 3 进行选择时，它会给我 -4195200 作为一个值。

有什么帮助吗？这是我的代码:

// This project will be a game of Rock, Paper, Scissors

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

// Function Prototypes
int choices();
int userselect (int, int);

int main()
{

        //Variables and Seed
        int selection;
        char again;
        unsigned seed = time(0);
        srand(seed);
        int compselect = (rand()%3)+1;

        //Constants for the menu choices
        const int ROCK = 1,
                  PAPER = 2,
                  SCISSORS = 3;

        do
        {
                //Display the menu choices and validate
                choices();

                cout << "You picked " << selection << endl;
                cout << "The computer picked " << compselect << endl;

                //Display the results
                userselect(selection, compselect);

                //Replay loop
                cout << "Do you want to play again? (Y/N)";
                cin >> again;
        }
        while (again == 'Y' || again == 'y');
        return 0;
}

//***********************************************************
// This function will display the menu choices and validate *
//***********************************************************

int choices()
{
        int selection;

        cout << "********************************\n";
        cout << "*   Please Select A Choice     *\n";
        cout << "*          1 - Rock            *\n";
        cout << "*          2 - Paper           *\n";
        cout << "*          3 - Scissors        *\n";
        cout << "********************************\n";
        cin >> selection;

        //Validate the selection
        while (selection < 1 || selection > 3)
        {
                cout << "ERROR: Enter a valid choice.";
                cin >> selection;
        }

        return selection;
}

//***********************************************************
// This function will display the menu choices and validate *
//***********************************************************

int userselect (int num1, int num2)
{
         // If user enters Rock
        if (num1 == 1)
        {
                if (num2 == 1)
                {
                        cout << "You picked Rock \n";
                        cout << "The computer picked Rock \n";
                        cout << " TIE! \n";
                }
                else if (num2 == 2)
                {
                        cout << "You picked Rock \n";
                        cout << "The computer picked Paper \n";
                        cout << "Paper beats Rock. YOU LOSE! \n";
                }
                else if (num2 == 3)
                {
                        cout << "You picked Rock \n";
                        cout << "The computer picked Scissors \n";
                        cout << " Rock beats Scissors. YOU WIN! \n";
                }
        }

        // If user enters Paper
        if (num1 == 2)
        {
                if (num2 == 1)
                {
                        cout << "You picked Paper \n";
                        cout << "The computer picked Rock \n";
                        cout << " Paper beats Rock. YOU WIN! \n";
                }
                else if (num2 == 2)
                {
                        cout << "You picked Paper \n";
                        cout << "The computer picked Paper \n";
                        cout << " TIE! \n";
                }
                else if (num2 == 3)
                {
                        cout << "You picked Paper \n";
                        cout << "The computer picked Scissors \n";
                        cout << " Scissors beats Paper. YOU LOSE! \n";
                }
}

        // If user enters Scissors
        if (num1 == 3)
        {
                if (num2 == 1)
                {
                        cout << "You picked Scissors \n";
                        cout << "The computer picked Rock \n";
                        cout << " Rock beats Scissors. YOU LOSE! \n";
                }
                else if (num2 == 2)
                {
                        cout << "You picked Scissors \n";
                        cout << "The computer picked Paper \n";
                        cout << "Scissors beat Paper. YOU WIN! \n";
                }
                else if (num2 == 3)
                {
                        cout << "You picked Scissors \n";
                        cout << "The computer picked Scissors \n";
                        cout << " TIE! \n";
                }
        }
}

Answer 1

你不是handling the newline that's still in the cin input stream ，并且您没有对因此失败的 cin >> 选择 进行任何错误检查。因为它失败了，selection 没有被赋予任何新值，而且由于您没有初始化它，您得到这个垃圾号码 -4195200。

如果您执行了一些错误检查，或者允许您在 while 循环中通过初始化 selection 完成其工作的错误检查，您就会看到这一点 到 0:

int selection = 0;

在 main() 中，您也完全无法存储调用 choices() 的结果。请记住，choices() 中的变量 selection 是一个局部变量，与 main() 中的变量 selection 不同)，您永远不会为其分配值，在此代码中:

selection = choices();