A variable can be defined as a memory location declared to store any kind of data (which may change many times during program execution).
It can also be defined as any quantity/entity which may vary during program execution.
Variables are the identifiers of a memory location.
To identify a variable (the declared memory location), it can be assigned a name – known as a variable name.
The name given to a variable is known as an identifier.
An identifier can be a combination of alphabets, digits, and underscore.
Syntax
datatype Variablename;
Examples
int mark;
float a,b,result;
Variable naming rules
It should be unique but not a keyword.
The first letter should be an alphabet.
White space, symbols, special characters are not allowed.
Underscore can use ( _ ).
Uppercase and lowercase letters are evaluated differently.
Variable initialization
Syntax
datatype variablename = size;
Examples
int sum=10;
int result=0, mark, sub=10;
const float pi=3.14;
In the first example the variable 'sum' is assigned with a value 10,which is called variable initialization.
In the second example, the variable 'result' is assigned with a value 0, the variable 'sub' with a value 10.but the variable 'mark' indicates a normal variable declaration. In the third example, the variable pi declares as a constant with value 3.14, which cannot be altered during the program run.