Private Variable assigning

This is a discussion on Private Variable assigning within the C++ Programming forums, part of the General Programming Boards category; I'm working on a program that will take user input to display how much change you have, a friend has, ...

  1. #1
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    Private Variable assigning

    I'm working on a program that will take user input to display how much change you have, a friend has, and you have together. The code is below.

    My problem is in my output. The output file shows the following:
    You have $-8.58993e+008.
    Your friend has $-8.58993e+008.
    Together you have $-1.71799e+009.

    Can you tell me what is causing it?

    Here is my class.
    Code:
    #pragma once
    class change
    {
    private:
    	int pennies;
    	int nickels;
    	int dimes;
    	int quarters;
    public:
    	change(void);
    	change(int p, int n, int d, int q);
    	~change(void);
    	void SetPennies(int p);
    	void SetNickels(int n);
    	void SetDimes(int d);
    	void SetQuarters(int q);
    	int GetPennies();
    	int GetNickels();
    	int GetDimes();
    	int GetQuarters();
    	double GetValue(change c);
    	change AddCoins(change c);
    };
    Here is my program.
    Code:
    #include <iostream>
    #include <fstream>
    #include "change.h"
    using namespace std;
    
    
    void header(ofstream &outfile);
    void ChangeInput(change c1, change c2);
    void PrintChange(ofstream &outfile, change c1, change c2, change c3);
    
    
    int main()
    {
    	ofstream outfile;
    	outfile.open("output.txt");
    
    
    	change c1, c2, c3;
    
    
    	ChangeInput(c1, c2);
    	c3 = c1.AddCoins(c2);
    
    
    	header(outfile);
    	PrintChange(outfile, c1, c2, c3);
    
    
    	system("pause");
    	return 0;
    }
    
    
    void header(ofstream &outfile)
    {
    	outfile << "Trey Brumley" << endl;
    	outfile << "CMPS 1063-201" << endl;
    	outfile << "Dr. Tina Johnson" << endl;
    	outfile << "April 1, 2013" << endl;
    	outfile << "Program 3 - Classes Extended" << endl;
    	outfile << "This program will further demonstrate the use of classes by using a class designed to convert monetary change into cents values." << endl;
    	outfile << "================================================================================================================================" << endl << endl;
    
    
    	return;
    }
    
    
    void ChangeInput(change c1, change c2)
    {
    	int p, n, d, q;
    	cout << "Please enter the number of coins you have (pennies, nickels, dimes, quarters):" << endl;
    	cin >> p >> n >> d >> q;
    	c1.SetPennies(p);
    	c1.SetNickels(n);
    	c1.SetDimes(d);
    	c1.SetQuarters(q);
    
    
    	cout << endl << "Please enter the number of coins your friend has (pennies, nickels, dimes, quarters):" << endl;
    	cin >> p >> n >> d >> q;
    	c2.SetPennies(p);
    	c2.SetNickels(n);
    	c2.SetDimes(d);
    	c2.SetQuarters(q);
    
    
    	return;
    }
    
    
    void PrintChange(ofstream &outfile, change c1, change c2, change c3)
    {
    	outfile << "You have $" << c1.GetValue(c1) << "." << endl;
    	outfile << "Your friend has $" << c2.GetValue(c2) << "." << endl;
    	outfile << "Together you have $" << c3.GetValue(c3) << "." << endl;
    
    
    	return;
    }
    
    
    change::change(void)
    {
    }
    
    
    
    
    change::~change(void)
    {
    }
    
    
    change::change(int p, int n, int d, int q)
    {
    	pennies = p;
    	nickels = n;
    	dimes = d;
    	quarters = q;
    }
    
    
    void change::SetPennies(int p)
    {
    	pennies = p;
    }
    
    
    void change::SetNickels(int n)
    {
    	nickels = n;
    }
    
    
    void change::SetDimes(int d)
    {
    	dimes = d;
    }
    
    
    void change::SetQuarters(int q)
    {
    	quarters = q;
    }
    
    
    int change::GetPennies()
    {
    	return pennies;
    }
    
    
    int change::GetNickels()
    {
    	return nickels;
    }
    
    
    int change::GetDimes()
    {
    	return dimes;
    }
    
    
    int change::GetQuarters()
    {
    	return quarters;
    }
    
    
    double change::GetValue(change c)
    {
    	double total;
    
    
    	total = c.pennies+(5*c.nickels)+(10*c.dimes)+(25*c.quarters)/100.0;
    
    
    	return total;
    }
    
    
    change change::AddCoins(change c)
    {
    	change ch;
    	ch.pennies = pennies + c.pennies;
    	ch.nickels = nickels + c.nickels;
    	ch.dimes = dimes + c.dimes;
    	ch.quarters = quarters + c.quarters;
    
    
    	return ch;
    }

  2. #2
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    One of the problems is that you are passing variables by value when you want to change the values. Remember passing by value "copies" the variable so any changes to this copy are lost when the function returns. For example the following snippet:
    Code:
    void ChangeInput(change c1, change c2)
    {
        int p, n, d, q;
        cout << "Please enter the number of coins you have (pennies, nickels, dimes, quarters):" << endl;
        cin >> p >> n >> d >> q;
        c1.SetPennies(p);
        c1.SetNickels(n);
        c1.SetDimes(d);
        c1.SetQuarters(q);
     
     
        cout << endl << "Please enter the number of coins your friend has (pennies, nickels, dimes, quarters):" << endl;
        cin >> p >> n >> d >> q;
        c2.SetPennies(p);
        c2.SetNickels(n);
        c2.SetDimes(d);
        c2.SetQuarters(q);
     
     
        return;
    }
    Any changes to the parameters are lost when the function returns. You probably want to pass these variables by reference.

    Jim

  3. #3
    and the hat of wrongness Salem's Avatar
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    > void ChangeInput(change c1, change c2)
    Look at passing these by reference.

    Your local changes are being lost when the function returns.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  4. #4
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    So do I just add the ampersands?

  5. #5
    and the hat of wrongness Salem's Avatar
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    Try it and see.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  6. #6
    Algorithm Dissector iMalc's Avatar
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    Also, that class does not warrant having a destructor. Just delete it.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  7. #7
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    I have to include the destructor as part of the assignment.

    Also, everywhere I put the ampersands, I get an error of some kind.

  8. #8
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    Show the modified code and the complete error message.

    Jim

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