How to Declare Variables?

A typical variable declaration is of the form: 

// Declaring a single variable
type variable_name;

// Declaring multiple variables:
type variable1_name, variable2_name, variable3_name;

A variable name can consist of alphabets (both upper and lower case), numbers, and the underscore ‘_’ character. However, the name must not start with a number. 

In the above diagram,  

datatype: Type of data that can be stored in this variable. 
variable_name: Name given to the variable. 
value: It is the initial value stored in the variable.  

Examples:  

// Declaring float variable
float simpleInterest; 

// Declaring integer variable
int time, speed; 

// Declaring character variable
char var;  

We can also provide values while declaring the variables as given below:

int a=50,b=100;  //declaring 2 variable of integer type    
float f=50.8;  //declaring 1 variable of float type     
char c='Z';    //declaring 1 variable of char type   

Variables in C++ is a name given to a memory location. It is the basic unit of storage in a program. 

• The value stored in a variable can be changed during program execution.
• A variable is only a name given to a memory location, all the operations done on the variable effects that memory location.
• In C++, all the variables must be declared before use.