Creating loop for functions-

[SweetLen]

Hello out there;
Thank you for taking the time to help.
I need to figure out how to create a loop for my functions.
1st needed to create a menu with choices
a- calculate mpg
b- calculate inflation rate
c- select the largest number of 2 parameters
d- select the largest number of 3 parameters
x- exit
This has been done, but I can only porperly access choices: A & X
I can access B, but it uses the calculation of "A", and
C & D are not accessible at all.
Plus, Choices A-D need to be made so the user can repeat the calculations as many times desired so.
Hence my next problem, not being able to properly place and create the loop for each section.
I would greatly appreciate the help.
Thnx in advance

#include<iostream>
#include<iomanip>
#include<string>
using namespace std;

// Prototypes
void errorMsg();
char UpCase(char);
void GetData(double&, double&);
void CalculateMPG(double, double, double&);
void DisplayMPG(double);

void GetPrices(double&, double&);
void CalculateInflationRate(double, double, double&);
void DisplayInflationRate(double);

void GetParameters(double&, double&);
void ReturnLargestValueI(double, double, double&);
void DisplayLargestValueI(double);

void GetValues(double&, double&, double&);
void ReturnLargestValueII(double, double, double, double&);
void DisplayLargestValueII(double);



int main()
{

	bool userNotDone = true; 
	char menuChoice;
	double fuel, 
		distance,
		mpg;
	double price1,
		price2,
		ir;
	double parameter1,
		parameter2,
		largestValue1;
	double value1,
		value2,
		value3,
		largestValue2;


	while (userNotDone)
	{
		system("cls");
		cout << "\n\n\n\n\n\n\n\n\n";
			cout << "\t\t\t\tMenu" << endl;
			cout << "\t\t\tA. Calculate miles per gallon" << endl;
			cout << "\t\t\tB. Calculate rate of Inflation" << endl;
			cout << "\t\t\tC. Identify the largest of two parameters" << endl;
			cout << "\t\t\tD. Identify the largest of three parameters" << endl;
			cout << "\t\t\tX. Exit Program" << endl;
			cout << "\t\t\tEnter Menu Choice ==> ";
			cin >> menuChoice;


		switch (UpCase (menuChoice))
		{
		case 'A': 
			GetData(fuel,distance);
			CalculateMPG(fuel,distance,mpg);//sned in fuel, distance and get mpg back
			DisplayMPG(mpg);
			break;
		case 'B':
			GetData(price1, price2);
			CalculateInflationRate(price1, price2, ir);
			DisplayInflationRate(ir);
			break;
		case 'C':
			GetParameters(parameter1, parameter2);
			ReturnLargestValueI(parameter1, parameter2, largestValue1);
			DisplayLargestValueI(largestValue1);
			break;
		case 'D':
			GetValues(value1, value2, value3);
			ReturnLargestValueII(value1, value2, largestValue2);
			DisplayLargestValueII(largestValue2);
			break;
		case 'X':
			userNotDone = false;
			system("pause");
			break;
		default:
			errorMsg();
		}
	}

	return 0;

}

void errorMsg()
{
	cout << "\n\n\t\t\tYou must enter A, B, C, D or X" << endl;
	system("pause");
}

char UpCase(char letter)
{
	if(letter >=97 && letter <= 122)
		letter-=32;
	return letter;
}

////////////////////////////////
//// Part I (Secion A)/////
//////////////////////////////

//Input 
void GetData(double& liters, double& miles) // get this number from input
{
	system("cls");
	cout << "Enter the number of liters consumed ==>";
	cin >> liters;
	cout << "Enter the number of miles traveled  ==>";
	cin >> miles;

}
//Process
void CalculateMPG(double liters, double miles, double& mpg)// this is the value (calculation)
{
	mpg = miles / (liters * 0.264179);
}
//Output
void DisplayMPG(double mpg) // pass mpg from above (display)
{
	cout << setprecision(2) << fixed;
	cout <<"Your mileage is " <<mpg << " miles per gallon\n\n\n";
	system("pause");
}

/////////////////////////////////
////Part (Section B)/////
///////////////////////////////
//Input
void GetPrices(double& price1, double& price2)
{
	system("cls");
	cout << "Enter price of item last year ==>";
	cin >> price1;
	cout << "Enter price of item this year ==>";
	cin >> price2;
}
//Process
void CalculateInflationRate(double price1, double price2, double&ir)
{
	ir= ((price2 - price1)/((price1)/100)); 
}
//Output
void DisplayInflationRate(double ir)
{
	cout << setprecision(2) << fixed;
	cout << "Your inflation rate is " <<ir << "\n\n\n";
	system("pause");
}

/////////////////////////////////
////Part III (Section C)/////
///////////////////////////////
//Input
void GetParameters(double& parameter1, double& parameter2)
{
	system("cls");
	cout << "Enter your first parameter  ==>";
	cin >> parameter1;
	cout << "Enter your second parameter ==>";
	cin >> parameter2;
}
//Process
void ReturnLargestValueI(double parameter1, double parameter2, double&largestValue1)
{
	if (parameter1 <= parameter2)
	{
		largestValue1 = parameter2;
	}
	else if (parameter2 <= parameter1)
	{
		largestValue1 = parameter1;
	}
}
//Output
void DisplayLargestValueI(double largestValue1)
{
	cout << "The largest number is " <<largestValue1 << "\n\n\n";
	system("pause");
}

/////////////////////////////////
////Part IV (Section D)/////
///////////////////////////////
//Input
void GetValues(double& value1, double& value2, double& value3)
{
	system("cls");
	cout << "Enter your first parameter  ==>";
	cin >> value1;
	cout << "Enter your second parameter ==>";
	cin >> value2;
	cout << "Enter your third parameter  ==>";
	cin >> value3;
}
//Process
void ReturnLargestValueII(double value1, double value2, double value3, double& largestValue2)
{
	if (value1 <= value2 && value2 <= value3)
	{
		largestValue2 = value3;
	}
	else if (value1 <= value3 && value3 <= value2)
	{
		largestValue2 = value2;
	}
	else if (value2 <= value1 && value1 <= value3)
	{
		largestValue2 = value3;
	}
	else if (value2 <= value3 && value3 <= value1)
	{
		largestValue2 = value1;
	}
	else if (value3 <= value1 && value1 <= value2)
	{
		largestValue2 = value2;
	}
	else if (value3 <= value2 && value2 <= value1)
	{
		largestValue2 = value1;
	}
}
//Output
void DisplayLargestValueII(double largestValue2)
{
	cout << "The largest number is " <<largestValue2 << "\n\n\n";
	system("pause");
}

[Tamao]

Hello, if you want the program to repeat the choices i suggest you wrap your switch() in a while loop that continues until a special condition has been met for example:

bool TrueOrFalse = false;
int i = 1;
while(!TrueOrFalse)
{
   //do something here
   if(i == 2)
   {
      TrueOrFalse = true;
   }
   ++i;
}

EDIT: you can use the same for the calculations

[Browni3141]

Please format your code with [code] tags. It will make your post more legible.