VARIABLES IN C++ | Define & Declare

VARIABLES IN C++

Declaration of variables.

C++ requires all the variables to be defined at the beginning of a scope. But C++ allows the declaration of variable anywhere in the scope. That means a variable can be declared right at the place of its first use. It makes the program easier to understand.

Dynamic initialization of variables.

In c++, a variable can be initialized at run time using expressions at the place of declaration. This is refereed to as dynamic initialization. 

Ex.- int m = 10; 

Here variable m is declared and initialized at the same time.

Reference variables.

i) A reference variable provides an alias for a previously defined variable.

ii) Example:- If we make the variable sum a reference to the variable total, them sum & total can be used interchangeably to represent that variable. 

iii) Reference variable is created as:- 

            data type & reference name = variable name. 

            Ex:- int sum = 200; int &total = sum; 

Here total is the alternative name declared to represent the variable sum. Both variable refer to the same data object in memory. 

iv) A reference variable must be initialized at the time of declaration. 

v) C++ assigns additional meaning to the symbol '&'.Here & is not an address operation. The notation int & means reference to int. A major application of reference variable is in passing arguments to functions.

Ex. void fun (int &x) // uses reference 

    { 

            x = x + 10; // x increment, so x also incremented. 

    } 

    int main( ) 

    { 

            int n = 10; fun(n); // function call 

    } 

When the function call fun(n) is executed, it will assign x to n 

            i.e. int &x = n; 

Therefore x and n are aliases & when function increments x. n is also incremented. This type of function call is called call by reference.

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