Exception Handling: if user input is not one of three specific characters - c++

Question

I'm working on a Rock Paper Scissors game in C++, and for my exception handling I'm trying to create an if statement for when the user input is not one of three characters, 'R', 'S' or 'P', but I just don't know how to properly build it without receiving error alerts.
I went to my textbook, my professor's videos on Exception Handling, and of course here on StackOverflow, to see if my issue has already been found (of which I've found none). I'm also not sure if I'm using throw correctly.
Here is my code:
#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

Your first three if statements are wrong. If both players don't enter R, you throw an error. The statements need to be rewritten to this instead:
if (Player1 != 'R' && Player1 != 'P' && Player1 != 'S')
throw 0;
if (Player2 != 'R' && Player2 != 'P' && Player2 != 'S')
throw 0;
I would suggest wrapping the input logic in some helper functions. And also, you can clean up the rest of the if statements as well.
Try this:
#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;
}
Alternatively, consider using a switch statement instead of multiple if statements:
#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;
}