c++ - 如何等待有效输入

Question

我正在重现一场战斗，它基于硬币，正面或反面。我让用户输入“H、h、T、t”来确定战斗。我的问题是我已经实现那些只能是有效输入，但是如果我输入“G”，例如，它显示无效输入但仍然执行。我怎样才能让我的程序等待这些有效输入之一？谢谢!

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <sstream>

using namespace std;

int main()

{
    //A little information about the battle

    cout << "\t\t\tLet the\n\n";
    cout << "Decision of heads or tails on the coin react history\n";

    cout << "\t\t/---------------------\\" << endl;
    cout << "\t\t| RETURN TO SEVEN DAYS|\n";
    cout << "\t\t\\---------------------/\n\n" << endl;

    //Main Battle

    cout << "It is July 1, 1862, the final day\n";
    cout << "of the Battle of Seven Days...\n\n";

    cout << "In this re-enactment of the second day\n";
    cout << "of battle, you are George B. McClellan\n";
    cout << "in charge of the Unionists\n\n";

    cout << "We will flip a coin to determine the\n";
    cout << "outcome of the small battles for\n";
    cout << "territories within the Seven Days area\n\n";

    cout << "You will have to predict whether the coin\n";
    cout << "will come up heads or tails...\n\n";

    cout << "In the actual Battle at Seven Days,\n";
    cout << "the Northern troops turned back Lee's\n";
    cout << "final assaults at Malvern Hill(July\n";
    cout << "1)....\n\n";

    cout << "The confederates lost about 16,000\n";
    cout << "men...\n\n";

    cout << "The Unionists lost about 20,000 men...\n\n";

    cout << "McClellan's failure to capture\n";
    cout << "Richmond, and the subsequent\n";
    cout << "withdrawal of the Union's Army from\n";
    cout << "the Yorktown Peninsula, signified the\n";
    cout << "end of the Peninsular Campaign\n\n";

    //Running through the battles

    int battleName = 1;

    for (; battleName <= 9; battleName += 1){

        cout << "Battle \t\n" << battleName << " - ";

        switch (battleName)
        {
        case 1: cout << "Oak Grove ";
            break;
        case 2: cout << "Mechanicsville ";
            break;
        case 3: cout << "Gaines Mill ";
            break;
        case 4: cout << "Garnett Farm ";
            break;
        case 5: cout << "Golding Farm ";
            break;
        case 6: cout << "The Peach Orchard ";
            break;
        case 7: cout << "Savage Station ";
            break;
        case 8: cout << "Frayser Farm ";
            break;
        case 9: cout << "Malvern Hill ";
            break;
        }

        //Asking the user for input

        cout << "\nNow Now, General McClellan\n";
        cout << "What do you predict the coin outcome will be, \n";
        cout << "Heads (H) or Tails (T)? \n";
        cout << "Please choose either Heads or Tails:\n";

        string userInput;

        cin >> userInput;

        if (userInput == "H" || userInput == "h")
            cout << "\n You have chosen heads!" << endl;

        if (userInput == "T" || userInput == "t")
            cout << "\n You have chosen tails!" << endl;

        else if (!(userInput == "H" || userInput == "h" || userInput == "T" || userInput == "t"))
            userInput = 'H';
            cout << "Invalid input. You must choose either heads or tails!\n";

        cout << "\t\tPlease get ready to fight, General McClellan!!\n\n\n";


        //random number function

    unsigned seed = time(0);
    srand (seed);

    //to integers, heads or tails

    const int MIN_VALUE = 0;
    const int MAX_VALUE = 1;
    int coin = 0;

        coin = (rand () % (MAX_VALUE - MIN_VALUE +1)) + MIN_VALUE;

    //Deciding the actual coin flip

    cout << "The result of the coin flip was ";

        if (coin == 0)
            cout << "heads!\n\n\n";

        if (coin == 1)
            cout << "tails!\n\n\n";


    //incrementing values of the winner

    int computerScore = 0;
    int score = 0;



    if(((userInput == "T" || userInput == "t") && coin == 1))
    {
        cout << "Well done, General \nMcClellan...\n You have defeated Lee!\n";
        score += 1;
    }

     else if(((userInput == "H" || userInput == "h") && coin == 0))
    {
        cout << "Well done, General \nMcClellan...\n You have defeated Lee!\n";
        score += 1;
    }

    else
    {
        cout << "I am sorry, General\nMcClellan...\n But the battle goes to Lee!";
            computerScore += 1;

    }

        cout << "\n So far: McClellan " << score << " victories,\n" << "Lee " << computerScore << "\n\n\n";



    //Scoring

    if (score > computerScore)
            cout << "The results show that\n George B. McClellan\nwon the majority of the battles\nand is thus declared the victor\non July 1 1862.\n\n\n";

    if (score < computerScore)
        cout << "The results show that\nRobert E Lee\nwon the majority of the battles\nand is thus declared the victor\non July 1 1862\n\n\n";

    }

    return 0;
}

Answer 1

这是最简单的方法，我会使用 char 作为输入。编辑:char 在这种情况下不起作用，这是我在用 C++ 编码时忘记的事情之一。

string userINput;
while ((cin >> userInput) != "H" && userInput != "h" &&
            userInput != "T" && userInput != "t");

然后我会去掉这段代码:

else if (!(userInput == "H" || userInput == "h" || userInput == "T" || userInput == "t"))
            userInput = 'H';
            cout << "Invalid input. You must choose either heads or tails!\n";

一起。

你在这里也有一个问题，你想执行 userInput = H 并在 else 之后打印消息，但你没有 {} 所以它应该是这样才能工作:

  else if (!(userInput == "H" || userInput == "h" || userInput == "T" || userInput == "t")) {
            userInput = 'H';
            cout << "Invalid input. You must choose either heads or tails!\n";
  }