*Reference variables & parameters
---------------------------------

In C++ it is posible to have more than 1 variable all sharing the same location in memory.
For example we could have another variable which also uses the same location in memory.
Such a variable is called a reference variable because it references or accesses the same 
value as another variable.


-------------
int number; //the original variable
number = 16; //store a value
int &ref_num = number; //create a reference to the variable
-------------

The use of the &, means that the variable ref_num is a reference to the variable number.
The two names ref_num and number both use the same memory location, and so control 
the same data.

-------------
cout << number << endl;
cout << ref_num << endl; //both lines print 16
num +=10; //increase by 10
cout << number << endl;
cout << ref_num << endl;
ref_num *=2;
cout << number << endl;
cout << ref_num << endl;
-------------

*Parameters in functions (passing by value)
-------------------------------------------
The C++ and C languages were written so that the default way in which parameters are passed
to functions, is passed by value. This means that when a function is called, the value 
(only) of the actual parameters is passed to the function. In other words, the function has
has to make a local copy of the data in a seperate memory location and can only work
on the copy.

-------------
#include<iostream.h>
void mystery(int num);
void main(void)
{
	int a = 6;
	cout << "the value of A is " << a << endl;
	mystery(a);
	cout << "the value of a is " << a << endl;
}
void mystery(int num)
{
	cout << "the value of num is " << num << endl;
	num = 82;
	cout << "the value of num is " << num << endl;
}


*Passing by reference
---------------------
#include<iostream.h>
void mystery(int &num);
void main(void)
{
	int a = 6;
	cout << "the value of a is " << a << endl;
	mystery(a);
	cout << "the value of a is " << a << endl;
}
void mystery(int &num)
{
	cout << "the value of num is " << num << endl;
	num = 82;
	cout << "the value of num is " << num << endl;
}
	
////////////////////////////////////////////////////////////////
Write a function which accepts a floating point parameter 
(by reference) and doubles that parameter.
-------------------------------
#include<iostream.h>
void double_num(float &num);
void main(void)
{
	float number;
	cout <<"enter a number ";
	cin >> number;
	double_num(number);
	cout << "the number is " << number << endl;
}
void double_num(float &num)
{
	cout << "the number is " << num << endl;
	num *=2;

}