Обработка исключений: если пользовательский ввод не является одним из трех определенных символов

Question

Я работаю над игрой Rock Paper Scissors на C ++, и для обработки исключений я пытаюсь создать оператор if для случая, когда пользовательский ввод не является одним из трех символов, 'R', 'S 'или' P ', но я просто не знаю, как его правильно построить, не получая оповещений об ошибках.

Я пошел в свой учебник, видео моего профессора по обработке исключений и, конечно, здесь, в StackOverflow, чтобы посмотреть, была ли моя проблема уже найдена (из которых я не нашел ни одной). Я также не уверен, правильно ли я использую throw.

Вот мой код:

#include <iostream>
#include <cctype>
using namespace std;

int main(int argc, const char * argv[]) {

    char Player1;
    char Player2;
    char playAgain = 'Y';

    do {            
        try {                
            cout << "Welcome to Rock Paper Scissors!" << endl;
            cout << "Player 1, you're up! Enter R, P, or S." << endl;
            cin >> Player1;
            Player1 = toupper(Player1);

            cout << "Now Player 2, make your move! R, P, or S." << endl;
            cin >> Player2;
            Player2 = toupper(Player2);

            if( Player1 != 'R' && Player2 != 'R')
                throw 0;

            else if(Player1 != 'S' && Player2 !='S')
                throw 0;

            else if(Player1 != 'P' && Player2 !='P')
                throw 0;

            if (Player1 == Player2)
                cout << "Tie game. Play again!";

            else if(Player1 == 'R' && Player2 == 'P')
                cout << "Paper covers rock, Player 2 wins!";

            else if(Player1 == 'R' && Player2 == 'S')
                cout << "Rock breaks scissors, Player 1 wins!";

            else if(Player1 == 'P' && Player2 == 'R')
                cout << "Paper covers rock, Player 1 wins!";

            else if(Player1 == 'P' && Player2 == 'S')
                cout << "Scissors cut paper, Player 2 wins!";

            else if(Player1 == 'S' && Player2 == 'R')
                cout << "Rock breaks scissors, Player 2 wins!";

            else if(Player1 == 'S' && Player2 == 'P')
                cout << "Scissors cut paper, Player 1 wins!";            
        }            
        catch(int errID) {
            cout << "Error: " << errID << endl;
        }

        cout << "Do you want to play again? Y/N ";
        cin >> playAgain;
        playAgain = toupper(playAgain);            
    }        
    while (playAgain == 'Y');            

    return 0;    
}

Answer 1

Ваши первые три if утверждения неверны. Если оба игрока не вводят R, вы выдаете ошибку. Утверждения должны быть переписаны к этому вместо:

if (Player1 != 'R' && Player1 != 'P' && Player1 != 'S')
    throw 0;
if (Player2 != 'R' && Player2 != 'P' && Player2 != 'S')
    throw 0;

Я бы предложил обернуть входную логику в некоторые вспомогательные функции. А также вы можете очистить и остальные операторы if.

Попробуйте это:

#include <iostream>
#include <cctype>
using namespace std;

char getInput(const char *prompt)
{
    char input;
    cout << prompt << ": ";
    if (!(cin >> input)) throw 1;
    return toupper(input);
}

char getChoice(const char *prompt)
{
    cout << prompt;
    char choice = getInput(" Enter R, P, or S");
    if ((choice != 'R') && (choice != 'P') && (choice != 'S')) throw 2;
    return choice;
}

int main(int argc, const char * argv[]) {

    char Player1;
    char Player2;

    cout << "Welcome to Rock Paper Scissors!" << endl;

    do {
        try {
            Player1 = getChoice("Player 1, you're up!");
            Player2 = getChoice("Now Player 2, make your move!");

            if (Player1 == Player2)
                cout << "Tie game!" << endl;

            else if (Player1 == 'R')
            {
                if (Player2 == 'P')
                    cout << "Paper covers rock, Player 2 wins!" << endl;        
                else
                    cout << "Rock breaks scissors, Player 1 wins!" << endl;
            }
            else if (Player1 == 'P')
            {
                if (Player2 == 'R')
                    cout << "Paper covers rock, Player 1 wins!" << endl;        
                else
                    cout << "Scissors cut paper, Player 2 wins!" << endl;
            }        
            else {
                if (Player2 == 'R')
                    cout << "Rock breaks scissors, Player 2 wins!" << endl;        
                else
                    cout << "Scissors cut paper, Player 1 wins!" << endl;
            }       
        }            
        catch (int errID) {
            cout << "Error: " << errID << endl;
        }
    }        
    while (getInput("Do you want to play again? Y/N") == 'Y');            

    return 0;    
}

В качестве альтернативы рассмотрите возможность использования оператора switch вместо нескольких операторов if:

#include <iostream>
#include <cctype>
using namespace std;

#define MAKE_USHORT(ch1, ch2) ((static_cast<unsigned short>(ch1) << 8) | static_cast<unsigned short>(ch2)) 

const char ROCK = 'R';
const char PAPER = 'P';
const char SCISSOR = 'S';

const unsigned short ROCK_ROCK = MAKE_USHORT(ROCK, ROCK);
const unsigned short ROCK_PAPER = MAKE_USHORT(ROCK, PAPER);
const unsigned short ROCK_SCISSOR = MAKE_USHORT(ROCK, SCISSOR);

const unsigned short PAPER_ROCK = MAKE_USHORT(PAPER, ROCK);
const unsigned short PAPER_PAPER = MAKE_USHORT(PAPER, PAPER);
const unsigned short PAPER_SCISSOR = MAKE_USHORT(PAPER, SCISSOR);

const unsigned short SCISSOR_ROCK = MAKE_USHORT(SCISSOR, ROCK);
const unsigned short SCISSOR_PAPER = MAKE_USHORT(SCISSOR, PAPER);
const unsigned short SCISSOR_SCISSOR = MAKE_USHORT(SCISSOR, SCISSOR);

char getInput(const char *prompt)
{
    char input;
    cout << prompt << ": ";
    if (!(cin >> input)) throw 1;
    return toupper(input);
}

char getChoice(const char *prompt)
{
    cout << prompt;
    char choice = getInput(" Enter R, P, or S");
    if ((choice != ROCK) && (choice != PAPER) && (choice != SCISSOR)) throw 2;
    return choice;
}

unsigned short getChoices()
{
    char Player1 = getChoice("Player 1, you're up!");
    char Player2 = getChoice("Now Player 2, make your move!");
    return MAKE_USHORT(Player1, Player2);
}

int main(int argc, const char * argv[]) {

    cout << "Welcome to Rock Paper Scissors!" << endl;

    do {
        try {
            switch (getChoices())
            {
                case ROCK_ROCK:
                case PAPER_PAPER:
                case SCISSOR_SCISSOR:
                    cout << "Tie game!" << endl;
                    break;

                case ROCK_PAPER:
                    cout << "Paper covers rock, Player 2 wins!" << endl;
                    break;

                case ROCK_SCISSOR:
                    cout << "Rock breaks scissors, Player 1 wins!" << endl;

                case PAPER_ROCK:
                    cout << "Paper covers rock, Player 1 wins!" << endl;
                     break;

                case PAPER_SCISSOR:
                    cout << "Scissors cut paper, Player 2 wins!" << endl;
                    break;

                case SCISSOR_ROCK:
                    cout << "Rock breaks scissors, Player 2 wins!" << endl;
                    break;

                case SCISSOR_PAPER:
                    cout << "Scissors cut paper, Player 1 wins!" << endl;
                    break;
            }       
        }            
        catch (int errID) {
            cout << "Error: " << errID << endl;
        }
    }        
    while (getInput("Do you want to play again? Y/N") == 'Y');            

    return 0;    
}