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Adding values within a loop

Jon15 (151)
I am writing a program that will calculate how much some selected foreign currency would cost in us dollars. I am having trouble getting started with the loop that will keep track and add all of it up once the user hits "0", or quits the program. Also, i am having trouble with restarting my program and inputting new values for the exchange rate, i.e. when the user wants to input a "9". 

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 #include "stdafx.h"
#include <iostream>
#include<cmath>

using namespace std;
using namespace System;
double eur2us();
double gbp2us();
double jpy2us();
double eur, gbp, jpy;
double us;


int main()
{
	double a;
	int choice;

	cout << "Welcome to my currency calculator!" << endl;
	while (choice != 0)
	{
		cout << "Please input the current exchange rate per US dollar of the following" << endl;
		cout << "EUR, GBP, JPY ";
		cin >> eur >> gbp >> jpy;
		do
		{
			cout << "Please input currency for valuation (1 = EUR 2 = GBP 3 = JPY 9 = NEW RATES \n0 = QUIT" << endl;
			cin >> choice;

			if (choice == 1)
			{
				a = eur2us();
				
			}
			else if (choice == 2)
			{
				a = gbp2us();
				
			}
			else if (choice = 3)
			{
				a = jpy2us();
				
			}
			else
			{
				cout << "Enter a valid key please" << endl;
			}
		} while (choice != 9);
	}
	system("pause");
    return 0;
}
double eur2us()
{
	double euros;
	

	cout<<"How many Euros are you buying?" << endl;
	cin >> euros;
	us = euros*eur;
	cout << "That will cost you "<<us<<" US dollars"<<endl;

	return us;
}
double gbp2us()
{
	double pounds;

	cout << "How many pounds of Sterling are you buying?" << endl;
	cin >> pounds;
	us = pounds*gbp;
	cout << "That will cost you "<<us<<" US dollars"<<endl;
	
	return us;
}
double jpy2us()
{
	double yen;
	cout << "How many Yen are you buying?" << endl;
	us = yen*jpy;
	cout << "That will cost you "<<us<<"US dollars"<<endl;

	return us;
}
Jon15 (151)
Ok, I fixed some problems but am still having trouble with my looping techniques. How do I add, and for some reason my 0 to quit isn't working anymore? 

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#include "stdafx.h"
#include <iostream>
#include<cmath>

using namespace std;
using namespace System;
double eur2us();
double gbp2us();
double jpy2us();
double eur, gbp, jpy;



int main()
{
	double a1, a2, a3;
	int choice = 8;
	double total = 0;

	cout << "Welcome to my currency calculator!" << endl;
	do
	{
		cout << "Please input the current exchange rate per US dollar of the following" << endl;
		cout << "EUR, GBP, JPY ";
		cin >> eur >> gbp >> jpy;
		do
		{
			cout << "Please input currency for valuation (1 = EUR 2 = GBP 3 = JPY 9 = NEW RATES \n0 = QUIT" << endl;
			cin >> choice;

			if (choice == 1)
			{
				a1 = eur2us();
				
			}
			else if (choice == 2)
			{
				a2 = gbp2us();
				
			}
			else if (choice == 3)
			{
				a3 = jpy2us();
				
			}
			else if (choice == 0)
			{
				cout << "Sorry that you wish to quit the program" << endl;
			}
			else
			{
				cout << "Enter a valid key please" << endl;
			}
		} while (choice != 9);
	} while (choice != 0);
	total = a1 + a2 + a3;
	cout << "The total amount in US dollars is " << total<<endl;
	cout << "Thank You for using my currency converting program!" << endl;
	system("pause");
    return 0;
}
double eur2us()
{
	double euros;
	bool valid = false;
	
	while (!valid)
	{
		valid = true;
		cout << "How many Euros are you buying?" << endl;
		cin >> euros;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value "<<endl;
			valid = false;
		}
		else if (euros < 0)
		{
			cout<<"Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us1 = euros*eur;
	cout << "That will cost you "<<us1<<" US dollars"<<endl;

	return us1;
}
double gbp2us()
{
	double pounds;
	bool valid = false;

	while (!valid)
	{

		valid = true;
		cout << "How many pounds of Sterling are you buying?" << endl;
		cin >> pounds;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (pounds < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	
	double us2 = pounds*gbp;
	cout << "That will cost you "<<us2<<" US dollars"<<endl;
	
	return us2;
}
double jpy2us()
{
	double yen;
	bool valid = false;

	while (!valid)
	{
		valid = true;
		cout << "How many Yen are you buying?" << endl;
		cin >> yen;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (yen < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us3 = yen*jpy;
	cout << "That will cost you "<<us3<<"US dollars"<<endl;

	return us3;
}
chicofeo (640)
I would delete the do/while loop. Specifically, line 21,line22, and line 55.

Take a look at line 54:
} while (choice != 9);

If you change it to:

} while (choice != 0);

Then it will close the program. I hope it helps.
Jon15 (151)
Yes thanks a lot. I am still stuck on how to add up the, presumably 3, values for calculated us prices and output that at end of main() ?
Jon15 (151)
Here is what I have so far, why doesn't this work? 

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using namespace std;
using namespace System;
void eur2us();
void gbp2us();
void jpy2us();
double eur, gbp, jpy;
double us1 = 0, us2 = 0, us3 = 0;


int main()
{
	
	int choice = 9;
	

	cout << "Welcome to my currency calculator!" << endl;
	while (choice == 9)
	{
		cout << "Please input the current exchange rate per US dollar of the following" << endl;
		cout << "EUR, GBP, JPY ";
		cin >> eur >> gbp >> jpy;
		do
		{
			cout << "Please input currency for valuation (1 = EUR 2 = GBP 3 = JPY 9 = NEW RATES \n0 = QUIT" << endl;
			cin >> choice;

			if (choice == 1)
			{
				eur2us();

			}
			else if (choice == 2)
			{
				gbp2us();

			}
			else if (choice == 3)
			{
				jpy2us();

			}
			else if (choice == 0)
			{
				cout << "Sorry that you wish to quit the program" << endl;
				break;
			}
			else
			{
				cout << "Enter a valid key please" << endl;
			}
		} while (choice != 9);

	}
	double total = us1 + us2 + us3;
	cout << "The total amount in US dollars is " << total<<endl;
	cout << "Thank You for using my currency converting program!" << endl;
	system("pause");
    return 0;
}
void eur2us()
{
	double euros;
	bool valid = false;
	
	while (!valid)
	{
		valid = true;
		cout << "How many Euros are you buying?" << endl;
		cin >> euros;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value "<<endl;
			valid = false;
		}
		else if (euros < 0)
		{
			cout<<"Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us1 = euros*eur;
	cout << "That will cost you "<<us1<<" US dollars"<<endl;

	return;
}
void gbp2us()
{
	double pounds;
	bool valid = false;

	while (!valid)
	{

		valid = true;
		cout << "How many pounds of Sterling are you buying?" << endl;
		cin >> pounds;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (pounds < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	
	double us2 = pounds*gbp;
	cout << "That will cost you "<<us2<<" US dollars"<<endl;
	
	return ;
}
void jpy2us()
{
	double yen;
	bool valid = false;

	while (!valid)
	{
		valid = true;
		cout << "How many Yen are you buying?" << endl;
		cin >> yen;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (yen < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us3 = yen*jpy;
	cout << "That will cost you "<<us3<<" US dollars"<<endl;

	return;
}
chicofeo (640)
I am posting your code with my recommended changes. I added the comments on my recommendations:

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#include "stdafx.h"
#include <iostream>
#include<cmath>

using namespace std;
using namespace System;
double eur2us();
double gbp2us();
double jpy2us();
double eur, gbp, jpy;



int main()
{
	double a1 = 0.0, a2 = 0.0, a3 = 0.0; // Initialize the variables.

	int choice = 8;
	double total = 0;

	cout << "Welcome to my currency calculator!" << endl;
	//do
	//{
		cout << "Please input the current exchange rate per US dollar of the following" << endl;
		cout << "EUR, GBP, JPY ";
		cin >> eur >> gbp >> jpy;
		do
		{
			cout << "Please input currency for valuation (1 = EUR 2 = GBP 3 = JPY 9 = NEW RATES \n0 = QUIT" << endl;
			cin >> choice;

			if (choice == 1)
			{
				a1 = eur2us();

			}
			else if (choice == 2)
			{
				a2 = gbp2us();

			}
			else if (choice == 3)
			{
				a3 = jpy2us();

			}
			else if (choice == 0)
			{
				cout << "Sorry that you wish to quit the program" << endl;
			}
			else
			{
				cout << "Enter a valid key please" << endl;
			}
                        
                        // Move it inside the while loop (next two lines).
			total = a1 + a2 + a3; 
			cout << "The total amount in US dollars is " << total << endl;

		} while (choice != 0);
	//} while (choice != 0);
	//total = a1 + a2 + a3; Old Location
	//cout << "The total amount in US dollars is " << total << endl; Old Location.
	cout << "Thank You for using my currency converting program!" << endl;
	system("pause");
	return 0;
}
double eur2us()
{
	double euros;
	bool valid = false;

	while (!valid)
	{
		valid = true;
		cout << "How many Euros are you buying?" << endl;
		cin >> euros;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value " << endl;
			valid = false;
		}
		else if (euros < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us1 = euros*eur;
	cout << "That will cost you " << us1 << " US dollars" << endl;

	return us1;
}
double gbp2us()
{
	double pounds;
	bool valid = false;

	while (!valid)
	{

		valid = true;
		cout << "How many pounds of Sterling are you buying?" << endl;
		cin >> pounds;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (pounds < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}

	double us2 = pounds*gbp;
	cout << "That will cost you " << us2 << " US dollars" << endl;

	return us2;
}
double jpy2us()
{
	double yen;
	bool valid = false;

	while (!valid)
	{
		valid = true;
		cout << "How many Yen are you buying?" << endl;
		cin >> yen;
		if (cin.fail())
		{
			cin.clear();
			cin.ignore();
			cout << "Please enter a valid currency value" << endl;
			valid = false;
		}
		else if (yen < 0)
		{
			cout << "Please enter a positive monetary value" << endl;
			valid = false;
		}
	}
	double us3 = yen*jpy;
	cout << "That will cost you " << us3 << "US dollars" << endl;

	return us3;
}


I hope it helps.
Last edited on
Jon15 (151)
Nevermind, I got it on my own. thanks for the help though!
chicofeo (640)
Good deal!
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