Reference Variable

Reference Variable

Explain reference variables.

· A reference variable provides a pat name (alternative name) for a previously defined variable.

o Syntax:

§ data-type & reference-name = variable-name

o Example:

§ float total = 100;

§ float & sum = total;

· Reference variable and variable can be used interchangeably to represent that variable.

· As shown in above example sum and total can use interchangeably. In the memory, Both the variable refers to the same data object.

· Reference variable initialized at the time of declaration.

· Most of application of reference variables is in passing arguments to functions.

Explain call by reference.

· Passing reference variable as an argument to the function is known as call by reference.

· In this, ‘formal’ arguments in the called function become ‘aliases’ to the ‘actual’ argument in the calling function.

· In this if any change it made with the function variable (alias) then it reflects to original variable (actual).

Example:

void swap (int & a, int & b) // a & b are ref variable

{

int t = a;
a = b;

b = t;

}

Void main()

{

Int X, Y;

X = 10;
Y = 20;

swap(X, Y);
cout << “\n X : “ << X;

cout << ”\n Y : “ << Y;

}

Output:

X : 20
Y : 10

· This function will exchange the value of m and n using their aliases (reference variable a and b).

Deference between call by value and call by reference.

Call by value	Call by reference.
In call by value mechanism we have to pass the variable as the argument to the function.	In call by reference mechanism we have to pass the reference of the variable as the argument to the function.
Syntax: return-type function-name (data-type variable-name) { . . . . . //function body}	Syntax: Return-type function-name (data-type & variable-name) { . . . . . //function body}
In call by value, if the value of the variable is change then it does not reflect to the original value of the variable.	In call by reference, if the value of the variable is change then it does reflect to the original value of the variable.
It creates the new set of variable for the function.	It does not create the new set of variable but the reference of the variable for the function.
Program occupies more memory if the call by value mechanism is used.	Program occupies less memory then the program uses the call by mechanism if the call by reference is used.