Thread: having a real tough time with functions..

I'm not sure why but some of the variable don't seem to pick up values. I'm having a hard time with functions, can't seem to grasp how pass values back and forth from main to the functions. sorry for the mess of a code and thanks for any help.

Code:

#include <iostream>
#include <iomanip>

using namespace std;

// function one, getting input 
void input(double &, double &, double &);

// function two, calculate interest rate and exits if the payment isn't enough
void interestRate (double &, double &, double &, double &, double &); 

// function three, the main working function, calculates the total interest, the final payments and the amount of months it takes.  
void calculations (int &, double &, double &, double &, double &, double &, double &);

// function four, display the results 

void results (int &, double &, double &); 

int main()  // all main does is call on the functions
{
	double money, interest, desiredPayment, realRate, totalInterest, finalPayment, monthlyInterest, minPay; 
	int months; 
	
	
	input(money, interest, desiredPayment);  
	
	interestRate(realRate, money, interest, desiredPayment, minPay); 

	calculations(months, monthlyInterest, totalInterest, money, realRate, finalPayment, desiredPayment); 

	results(months, totalInterest, finalPayment); 

	return 0; 
}

// this function gets the input from the user and puts it into reference variables. 

void input (double &money, double &interest, double &desiredPayment)
{
 
	cout << "How much do you want to borrow? $" ; 
	cin >> money ;	
		while (money <= 0)
		{	
			cout << "You must enter a positive number!\n"; 
			cout << "How much do you want to borrow? $"; 
			cin >> money ; 
		}
		cout << "What is the annual interest rate expressed as a percent? "; 
		cin >> interest; 
		while (interest <= 0) 
		{
			cout << "You must enter a positive number!\n"; 
			cout << "What is the annual interest rate expressed as a percent? "; 
			cin >> interest; 
		}
		cout << "What is the monthly payment amount? $"; 
		cin >> desiredPayment;
		while (desiredPayment <= 0) 
		{
			cout << "You must enter a positive number!\n"; 
			cout << "What is the monthly payment amount? $";
			cin >> desiredPayment; 
		}
}




// this function calculates the interest rate, and notifies if the minimum monthly payment isn't sufficient.

void interestRate (double &desiredPayment, double &money, double &interest, double &realRate, double &minPay )
{
	realRate = money *(interest/1200.0); // for some reasong realRate stays 0 
	 
	if (desiredPayment <= realRate)
	{
		minPay = realRate + 1 ; 
		cout << fixed << showpoint << setprecision(2);
		cout << "You must make  payments of at least $" << minPay << endl;
		cout << "Because your monthly interest is $" << realRate; 
		cout << endl;
		cout << endl; 
		cout << "** Don't get overwhelmed with debt! **\n\n"; 
		exit(0); 
	}
	else
		realRate = money *(interest/1200.0);
		
}
// This is the workhorse function, it calculates how many months it will take to pay off the loan, 
// what the final payment will be, 
// how much interest was payed over time, 
void calculations (int &months, double &monthlyInterest, double &totalInterest, double &money, double &realRate, double &finalPayment, double &desiredPayment)
{
	months = 1 ;
		while (desiredPayment <= money) 
		{
			monthlyInterest = money * realRate ;
			totalInterest = monthlyInterest + totalInterest ;
			money = money - desiredPayment ;
			months ++ ;
		}
		money = finalPayment ;
}
// This function displays the results 
void results (int &months, double &totalInterest, double &finalPayment) 
{
	cout << fixed << showpoint << setprecision(2);
	cout << "Your debt will be paid off after "<< months << "months, with a final payment of just " << finalPayment ; 
	cout << " The total amount of interest you will pay during that time is " << totalInterest << "\n\n";
	cout << "** Don't get overwhelmed with debt! **\n\n";
}

notice the parameters you pass when you call interestRate:

Code:

interestRate(realRate, money, interest, desiredPayment, minPay);

and notice how the parameters are defined in the function:

Code:

void interestRate (double &desiredPayment, double &money, double &interest, double &realRate, double &minPay )

if after fixing this you still have a problem, check to see if you did something similar in another function.

do you mean that I need to correct their order? or that I need to put & in front of them?

fix the order

Originally Posted by simstim99

do you mean that I need to correct their order? or that I need to put & in front of them?

Do you understand what the '&' is doing? If not, you probably don't need it.

it worked, thanks for your help!!!

also, I understand what the "&" means but thanks for your input as well.