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Menu with error checking

rantiv (101)
This program uses functions to simulate Plinko. Our menu function should error check but doesnt do it when a string is entered. So how would I override a string so that it continues to loop out our prompt?

Input:
-13
junk
-1
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0

Expected Output:
Welcome to the Plinko simulator!

Menu: Please select one of the following options:

0 - Quit the program
1 - Drop a single chip into one slot
2 - Drop multiple chips into one slot
3 - Drop multiple chips into each slot

Enter your selection now:
Invalid selection. Please enter 0, 1, 2 or 3
Enter your selection now:
Invalid selection. Please enter 0, 1, 2 or 3
Enter your selection now:
Invalid selection. Please enter 0, 1, 2 or 3
Enter your selection now:
Invalid selection. Please enter 0, 1, 2 or 3
Enter your selection now:
Goodbye!

Our Output:

Welcome to the Plinko simulator!

Menu: Please select one of the following options:

0 - Quit the program
1 - Drop a single chip into one slot
2 - Drop multiple chips into one slot
3 - Drop multiple chips into each slot

Enter your selection now:
Invalid selection. Please enter 0, 1, 2 or 3
Goodbye!

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#include <iostream>
#include <string>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <iomanip>

using namespace std;

const double PRIZE_0 = 100.00;
const double PRIZE_1 = 500.00;
const double PRIZE_2 = 1000.00;
const double PRIZE_3 = 0.00;
const double PRIZE_4 = 10000.00;
const double PRIZE_5 = 0.00;
const double PRIZE_6 = 1000.00;
const double PRIZE_7 = 500.00;
const double PRIZE_8 = 100.00;
const double CHANGE_LEFT_RIGHT = 0.5;
const int ROWS_OF_PEGS = 12;
const int PRECISION = 1;
const int SLOT_0 = 0;
const int SLOT_1 = 1;
const int SLOT_2 = 2;
const int SLOT_3 = 3;
const int SLOT_4 = 4;
const int SLOT_5 = 5;
const int SLOT_6 = 6;
const int SLOT_7 = 7;
const int SLOT_8 = 8;

//MENU FUNCTION

void OutputMenu() {
	cout << "Menu: Please select one of the following options:" << endl << endl;
	cout << "0 - Quit the program" << endl;
	cout << "1 - Drop a single chip into one slot" << endl;
	cout << "2 - Drop multiple chips into one slot" << endl;
	cout << "3 - Drop multiple chips into each slot" << endl << endl;
	cout << "Enter your selection now: " << endl;
	//cin >> menuChoice;
}
bool menuError(int& menuChoice) {
	//int menuChoice = 0;
	while (menuChoice > 3 || menuChoice < 0)
	{
		cout << "Invalid selection.  Please enter 0, 1, 2 or 3" << endl; //invalid selection change
		cin >> menuChoice;

	}
   return false;
}
/*
bool MenuError(int menuChoice) {
do {
//(menuChoice < 0 || menuChoice > 3)
cout << "Enter your selection now: " << endl;
cin >> menuChoice;
if(menuChoice < 0 || menuChoice > 3) {
cout << "Invalid selection.  Please enter 0, 1, 2 or 3" << endl;
return true;

}
else {
return false;

}
//cout << "Enter your selection now: " << endl;

} while(menuChoice < 0 || menuChoice > 3);
}
*/

/*void SlotNumberError(int slotNumber) {
double slotNumberDouble = 0.0;
double chipLocation = 0.0;
double totalWinnings = 0.0;
if (slotNumber > 8 || slotNumber < 0) {
cout << endl;
cout << "WRONG: FIXME!" << endl;
//break;
}

}*/

// void OutputPath (double chipLocation);
double DropChip(int chipLocation, bool outputPath);
double DropMultipleChips(int chipLocation, int numChips);
double ComputeWinnings(int chipLocation);

//REWARDS FUNCTION

double ComputeWinnings(int chipLocation) {
	double winnings = 0;

	switch (chipLocation) { // The prize won by user

	case SLOT_0:
	case SLOT_8:
		winnings = PRIZE_0;
		break;
	case SLOT_1:
	case SLOT_7:
		winnings = PRIZE_1;
		break;
	case SLOT_2:
	case SLOT_6:
		winnings = PRIZE_2;
		break;
	case SLOT_3:
	case SLOT_5:
		winnings = PRIZE_3;
		break;
	case SLOT_4:
		winnings = PRIZE_4;
		break;

		return winnings;
	}
}

//MAIN FUNCTION

int main() {
	srand(42);

	double slotNumberDouble = 0.0;
	double chipLocation = 0.0;
	double chipLocation2 = 0.0;
	double totalWinnings = 0.0;
	double averageWinningsPerChip = 0.0;
	int menuChoice = 0;
	int slotNumber = 0;
	int randomNumber = 0;
	int finalLocationChip1 = 0;
	int finalLocationChip2 = 0;
	int chipNumber = 0;
	int slotNumber2 = 0;

	cout << "Welcome to the Plinko simulator!" << endl << endl;

	do { // The menu options 
		do {
			OutputMenu();
			cin >> menuChoice;
			//MenuError(menuChoice);
		} while (menuError(menuChoice));

		switch (menuChoice) {
		case 1: // If user enters menu option 1
			cout << "*** Drop single chip ***" << endl << endl;
			cout << "Which slot do you want to drop the chip(s) in (0-8)? ";
			cin >> slotNumber;
			//SlotNumberError(slotNumber);
			slotNumberDouble = slotNumber;
			cout << fixed << setprecision(1) << endl;
			//cout << "*** Dropping chip into slot " << slotNumber << " ***";
			cout << endl;
			//cout << "Path: [" << slotNumberDouble;
			chipLocation = slotNumber;
			totalWinnings = DropChip(chipLocation, true);
			break;

		case 2: // If menu option 2 is chosen
			cout << "*** Drop multiple chips ***" << endl << endl;
			cout << "How many chips do you want to drop (>0)? " << endl;
			cin >> chipNumber;
			if (chipNumber < 1) {
				cout << "Invalid number of chips." << endl << endl;
				break;
			}
			else {
				cout << "Which slot do you want to drop the chip(s) in (0-8)? " << endl;
				cin >> slotNumber2;
				if (slotNumber2 > 8 || slotNumber2 < 0) {
					cout << "Invalid slot.";
					cout << endl << endl;
					break;
				}
				else {
					totalWinnings = 0;
					for (int i = 0; i < chipNumber; i++) { // The path of the multiple chips
						chipLocation = slotNumber2;
						totalWinnings += DropChip(chipLocation, false);
					}
					cout << fixed << setprecision(2);
					cout << "Total winnings on " << chipNumber << " chips: " << totalWinnings << endl;
					averageWinningsPerChip = totalWinnings / chipNumber;
					cout << "Average winnings per chip: " << averageWinningsPerChip << endl << endl;
				}
			}
			break;

			/* case 3: //multiple chips in multiple slots
			cout << "3 - Drop multiple chips into each slot" << */
		case 0: // If menu option 0 is chosen
			cout << "Goodbye!";

			return 0;
			break;
			//default:
			//cout << "Invalid selection.  Please enter 0, 1 or 2" << endl << endl;
			//break;
		}
	} while (true);

	return 0;
}

double DropChip(int chipLocation, bool outputPath = false) {
	double winnings = 0;
	int randomNumber = 0;
	double pathChipLocation = chipLocation;
	string path = "";

	if (outputPath) {
		//cout << "[";
	}
	for (int i = 0; i < ROWS_OF_PEGS; i++) { // The path of the chip
		if (pathChipLocation == 0) {
			pathChipLocation += CHANGE_LEFT_RIGHT;
		}
		else if (pathChipLocation == 8) {
			pathChipLocation -= CHANGE_LEFT_RIGHT;
		}
		else if (pathChipLocation > 0 || chipLocation < 8) {
			randomNumber = rand() % 2;
			if (randomNumber == 0) {
				pathChipLocation -= CHANGE_LEFT_RIGHT;
			}
			else {
				pathChipLocation += CHANGE_LEFT_RIGHT;
			}
		}
		else {
			pathChipLocation = pathChipLocation;
		}
		if (outputPath) {
			//cout << " " << fixed << setprecision(PRECISION) << pathChipLocation;
		}
	}

	if (outputPath) {
		//cout << "]";
	}
	chipLocation = static_cast<int>(pathChipLocation);

	switch (chipLocation) { // The prize won by user
	case SLOT_0:
	case SLOT_8:
		winnings = PRIZE_0;
		break;
	case SLOT_1:
	case SLOT_7:
		winnings = PRIZE_1;
		break;
	case SLOT_2:
	case SLOT_6:
		winnings = PRIZE_2;
		break;
	case SLOT_3:
	case SLOT_5:
		winnings = PRIZE_3;
		break;
	case SLOT_4:
		winnings = PRIZE_4;
		break;
	}
	if (outputPath) {
		cout << endl;
		cout << "Winnings: $" << fixed << setprecision(2) << winnings << endl << endl;
	}
	return winnings;
}
gunnerfunner (2127)
Handy Andy (5051)
Hello rantiv,

Your function menuError(int& menuChoice) although on the right track it is in the wrong place. The function requires an int, but if your input was not an int it will cause big problems. First at line 145 you are getting the input from the menu options. The "cin >> menuChoice;" is formatted and expecting an integer to be entered, but if a letter is entered "cin" will fail and not be usable again until it is cleared. Then you will be trying to send bad information to "menuError()".

It would work better to scrap the "menurror()" function and move its contents to "OutputMenu()". Then I would write "OutputMenu()" like this:

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int OutputMenu()
{
	int menuChoice{ 0 };

	std::cout << "Menu: Please select one of the following options:" << std::endl << std::endl;
	std::cout << "0 - Quit the program" << std::endl;
	std::cout << "1 - Drop a single chip into one slot" << std::endl;
	std::cout << "2 - Drop multiple chips into one slot" << std::endl;
	std::cout << "3 - Drop multiple chips into each slot" << std::endl << std::endl;
	std::cout << "Enter your selection now: " << std::endl;
	std::cin >> menuChoice;

	while (!std::cin)
	{
		std::cout << "Invalid selection.  Please enter 0, 1, 2 or 3" << std::endl; //invalid selection change
		std::cin.clear();
		std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
		std::cin >> menuChoice;
	}

	while (menuChoice > 3 || menuChoice < 0)
	{
		std::cout << "Invalid selection.  Please enter 0, 1, 2 or 3" << std::endl; //invalid selection change
		std::cin >> menuChoice;

	}

	return menuChoice;
}


Notice I changed the return value of the function and added the return statement at the end. And line 17 requires the header file "limits".

In main the inner "do while" loop at lines 143 to 147 is not needed because that is handled in the "OutputMenu" function. Just the call to "OutputMenu();" is needed.

Hope that helps,

Andy
dhayden (5798)
Andy's code won't work if you enter an invalid number followed by a word (like "6" followed by "junk". I think this fixes it:

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    while (! ((std::cin >> menuChoice) && menuChoice >= 0 && menuChoice < 4)) {
        std::cout << "Invalid selection.  Please enter 0, 1, 2 or 3" << std::endl;
        std::cin.clear();
        std::cin.ignore(std::numeric_limits < std::streamsize >::max(), '\n');
        }
    }


I often find that you can't do all the validation in the while condition. In those cases, it's usually clearer to break out of the middle of the loop:
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while (true) {
    get the input;
    if (input is valid) {
        break;
    } else {
        print an appropriate error message
}

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