Passing Objects

[Duki]

Hey everyone.

I need to write program that builds an object of Pizza class and then pass that object to Order class.

here's my Pizza class:

class Pizza
{
public:
    void setCheeseToppings ( int ) ;
    void setPepperoniToppings ( int ) ;
    void setSize ( string ) ;
    void setType ( string ) ;
private:
    int cheeseTop ;
    int pepperoniTop ;
    string size [ 3 ] = { "small" , "medium" , "large" } ;
    string type [ 3 ] = { "hand tossed" , "pan" , "deep dish" } ;
} ;

I know this is a general question, but how should my order.addPizza function look? Do I need to put the same variables that were in pizza into the orders class to store them or do i have access to those variables since the object has been passed?

I'm stuck here:

class Order
{
public:
    void addPizza ( Pizza ) ;
    void outOrder ( ) ;
private:
} ;

[Ancient Dragon]

If Order can contain one or many pizzas then it should have a vector of pizza objects, and pass the Pizza object by referenct so prevent unnecessary duplication of the object.

class Order
{
public:
    void addPizza ( Pizza& order) ;
    void outOrder ( ) ;
private:
    vector<Pizza> theOrders;
} ;

[Duki]

Oh ok. So how would I access the Pizza data to output it?

[Ancient Dragon]

a vector is a c++ array class, so just use a loop to access each Pizza object

int n = theOrders.size(); // get number of elements in the array
for(int i = 0; i < n; i++)
{
   outOrder(theOrders[i]);
}

You will want to add a parameter to outOrder function, similar to the parameter to addPizza().

[Narue]

>So how would I access the Pizza data to output it?
Probably define a member function or overloaded << operator that performs the output. In the code you posted, the Pizza class doesn't provide any way to get at the data. For example (keeping it simple):

class Pizza
{
public:
    void setCheeseToppings ( int ) ;
    void setPepperoniToppings ( int ) ;
    void setSize ( string ) ;
    void setType ( string ) ;

    template <typename CharT>
    friend std::basic_ostream<CharT>& operator<< (
      std::basic_ostream<CharT>& out, const Pizza& pie );
private:
    int cheeseTop ;
    int pepperoniTop ;
    string size;
    string type;
} ;

template <typename CharT>
std::basic_ostream<CharT>& operator<< (
  std::basic_ostream<CharT>& out, const Pizza& pie )
{
  return out<<"Cheese: "<< ( cheeseTop ? "Yes" : "No" );
}

[Duki]

Ok, so in my outOrders function would I be able to do something like:

cout << MyPizza.size << endl :

?

[Narue]

>cout << MyPizza.size << endl
No, size is a private data member. Unless the outOrders function is a friend of the Pizza class or a member function of a class which is a friend of the Pizza class, you don't have access to the private data. However, if you define the operator as I showed, you can do this:

cout<< MyPizza <<'\n';

And all of the private data you choose to output in the overloaded operator will be sent to cout in the way you format it, followed by a newline. Another example, even simpler:

#include <iostream>
#include <ostream>

class Time {
  int _minutes;
  int _seconds;
  bool _is_am;
public:
  Time ( int minutes, int seconds, int is_am )
    : _minutes ( minutes ), _seconds ( seconds ), _is_am ( is_am )
  {}

  friend std::ostream& operator<< ( std::ostream& out, const Time& t );
};

std::ostream& operator<< ( std::ostream& out, const Time& t )
{
  return out<< t._minutes <<':'<< t._seconds <<' '
    << ( t._is_am ? "AM" : "PM" );
}

int main()
{
  Time now ( 9, 55, true );

  std::cout<<"The time is "<< now <<". Isn't that nifty.\n";
}

[Duki]

is this

friend std::ostream& operator<< ( std::ostream& out, const Time& t );

the same as this

friend cout << ( ostream & out , const Time & t )

? Or am I utterly confused

template <typename CharT>
std::basic_ostream<CharT>& operator<< ( std::basic_ostream<CharT>& out, const Pizza& pie )

none of that^ makes since to me. =(

[Duki]

here's my updated .h file if that will help:

#pragma once

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

class Pizza
{
public:
    void setCheeseToppings ( int ) ;
    void setPepperoniToppings ( int ) ;
    void setSize ( istream & is ) ;
    void setType ( istream & is ) ;
private:
    int cheeseTop ;
    int pepperoniTop ;
    string size ;
    string type ;
} ;

class Order
{
public:
    void addPizza ( Pizza ) ;
    void outOrder ( ) ;
private:
} ;

example main:

int main()
{
    Order myOrder;                    // variable declarations
    Pizza cheesy;
    Pizza pepperoni;

    cout << "Cheese size type:  " << endl ;
    cheesy.setCheeseToppings(3);    // specify pizza
    cheesy.setSize( cin );
    cheesy.setType( cin );

    cout << "pep size type:  " << endl ;
    pepperoni.setSize( cin );        // specify pizza
    pepperoni.setPepperoniToppings(2);
    pepperoni.setType( cin );
    
    cout << pepperoni.size << endl << pepperoni.type << endl ;
    cout << cheesy.size << endl << cheesy.type << endl ;

    myOrder.addPizza(cheesy);        // add to order
    myOrder.addPizza(pepperoni);

    myOrder.outputOrder();            // ouput order
    cout << "\n -- Done! --\n";
    return 0;
}

[Narue]

>Or am I utterly confused
You're utterly confused. All of the things that cout can print have an operator<< defined for them. When you want to use this syntax to print your own custom classes:

cout<< my_object <<endl;

You have to overload the operator<< function for your class. The operator<< function should look like this for any given class and output stream:

[I]<output stream>[/I]& operator<< ( [I]<output stream>[/I]& out, const [I]<your class>[/I]& obj );

However, if you want the operator to have access to any private or protected members of the class, it has to be a friend of the class as well.

>friend cout << ( ostream & out , const Time & t )
I don't even know what this is supposed to be.

>none of that^ makes since to me. =(
It's the same thing, just more flexible because you're not restricted to std::ostream objects. For example, you can use both cout and wcout where the example that uses std::ostream can only use cout.

[Duki]

oh Ok, but how do classes access variables in other classes?

If my question isn't clear, maybe look at my example main() and see what I'm trying to do. I am completely lost on how to write the Orders class so that I can output the Pizza information. :(

I need to use a vector in the Orders class to store the pizza objects and then output them with the output func

[Narue]

>but how do classes access variables in other classes?
There are

1) Make the data members public, then anyone can access them:

class test {
public:
  int foo;
};

int main()
{
  test t;
  t.foo = 123;
}

2) Make the data members protected, then derived classes can access them:

class test {
protected:
  int foo;
};

class derived: public test {
public:
  void bar() { foo = 123; }
};

3) Make the function or class that accesses a data member a friend of the class:

class test {
  friend void bar ( test& t );
  friend class baz;
private:
  int foo;
};

void bar ( test& t )
{
  t.foo = 123;
}

class baz {
public:
  void blah ( test& t ) { t.foo = 123; }
};

4) Provide a public or protected member function that accesses the data member:

class test {
private:
  int foo;
public:
  int get_foo() { return foo; }
  void set_foo ( int value ) { foo = value; }
};

int main()
{
  test t;

  t.set_foo ( 123 );
  int bar = t.get_foo();
}

>I am completely lost on how to write the Orders class so that I can output the Pizza information.
Okay, a pizza contains all of its information, right? And an order is just a collection of pizzas. So what you want to do is have the Pizza class provide a way to print or return its information so that the Orders class can use that information. Like this (I'll even eschew the operator overloading as that seems to confuse you):

#include <iostream>
#include <string>
#include <vector>

class Pizza {
  std::string _name;
public:
  Pizza ( std::string name )
    : _name ( name )
  {}

  void display() const
  {
    std::cout<< _name <<'\n';
  }
};

class Orders {
  std::vector<Pizza> _pizzas;
public:
  void add_pizza ( const Pizza& pie )
  {
    _pizzas.push_back ( pie );
  }

  void display() const
  {
    std::vector<Pizza>::const_iterator it = _pizzas.begin();
    std::vector<Pizza>::const_iterator end = _pizzas.end();

    while ( it != end ) {
      it->display();
      ++it;
    }
  }
};

int main()
{
  Orders my_order;

  my_order.add_pizza ( Pizza ( "Chef Special" ) );
  my_order.add_pizza ( Pizza ( "Meat Lovers" ) );
  my_order.add_pizza ( Pizza ( "Veggie Lovers" ) );

  my_order.display();
}

It's just that easy.

[Duki]

Oh ok! that makes perfect sense! The only part I'm consfused about is this

it->display();

what is 'it->'

the -> operator lets us access a member of the structure pointed to by a pointer

And you don't necessarily need to use iterators loop through a vector. You can loop through it as you would a normal array using indexing.
http://www.cprogramming.com/tutorial/stl/iterators.html

[Duki]

That's a pointer?

If you want to think of it like that sure whatever floats your boat

[Duki]

I don't get it..... we haven't went over pointers yet :(

what?

[Narue]

>That's a pointer?
It's a pointer-like object.

>I don't get it..... we haven't went over pointers yet
Then do this:

void display() const
{
  std::vector<Pizza>::size_type i;

  for ( i = 0; i < _pizzas.size(); i++ )
    _pizzas[i].display();
}

[Duki]

thanks for all the help Narue! My program is working (almost) great!

I've just got a logic error somewhere that I'm trying to figure out. for some reason, when I output the Pepperoni pizza it outputs 1 cheese topping every time.

[Duki]

Alright, nvm got it. Leaving variables uninitialized = bad.