Page 57 - DCAP404 _Object Oriented Programming

Object-oriented Programming

Notes 2.6.4 Reference Variables

C++ introduces a new kind of variable known as the reference variable. A reference variable
provides an alias (alternative name) for a previously defined variable. For example, if we make
the variable sum a reference to the variable total, then sum and total can be used interchangeably
to represent that variable. A reference variable is created as follows:

data_type & reference_name = variable_name

Example:

float total = 100;
float &sum = total;
total is a float type variable that has already been declared, sum is the alternative name declared
to represent the variable total. Both the variables refer to the same data object in the memory.
Now, the statements
cout << total;
and

cout << sum;
both print the value 100. The statement
total = total + 10;
will change the value of both total and sum to 110. Likewise, the assignment
sum = 0;
will change the value of both the variables to zero.
A reference variable must be initialized at the time of declaration. This establishes the
correspondence between the reference and the data object that it names. Note that the initialization
of a reference variable is completely different from assignment.
Note that C++ assigns additional meaning to the symbol &. Here, & is not an address operator.
The notation float & means reference to float. Some more examples are presented below to
illustrate this point:
int n[10];
int &x = n[10]; //x is alias for n[10]
char &a = ‘\n’; // initialize reference to a literal
The variable x is an alternative to the array element n[10]. The variable a is initialized to the new
line constant. This creates a reference to the otherwise unknown location where the new line
constant \n is stored.
The following references are also allowed:
1. int x;
int *p=&x;
int &m = *p;

2. int &n = 50;

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