Variable in C

Variable:

    A quantity whose value can be changed during the execution of a program.

  e.g

  int a;

  a=3;

  a=5;

  a=10;

• During the execution 2 bytes are reserved for variable a
• During execution memory location’s name remains same but data can be changed.  

Rules for writing variable name: 

• First character must be an alphabet.
• ‘_’ can also be used as a first character.
•   Blank spaces not allowed.
•  Special characters can’t be used as a variable names
•   Reserved words(e.g int , float, char, bool , if , else, switch etc ) can’t be used as a variable name.
•  Variable name with one data type can’t be used for another data type.
•  C is a case sensitive language.
    int s
    int S 
    these are two different variables
  Are they are Variable Names or not: 
  
  • blac k 
  • Naeem 
  • jack et-1
  • Int
  • Num_1
  • If
  • Char
  • A
  • Ab
  • A1
  • A 2

How to use const with variable: 

 1. const float pi=3.14;

  2. Variable pi gets value 3.14 that can’t be changed.