Variables in C

A variable is a name of memory location. It is used to store data. Its value can be changed and it can be reused many times.

Rules for naming C variable:

  1. Variable name must begin with letter or underscore.
  2. Variables are case sensitive
  3. They can be constructed with digits, letters.
  4. No special symbols are allowed other than underscore.
  5. sum, height, _value are some examples for variable name

Declaring & initializing C variable:

  • Variables should be declared in the C program before to use.
  • Memory space is not allocated for a variable while declaration. It happens only on variable definition.
  • Variable initialization means assigning a value to the variable.

There are many types of variables in c:

  1. local variable
  2. global variable
  3. static variable
  4. automatic variable
  5. external variable

Local Variable

A variable that is declared inside the function or block is called local variable.

You must have to initialize the local variable before it is used.


Global Variable

A variable that is declared outside the function or block is called global variable. Any function can change the value of the global variable. It is available to all the functions.


Static Variable

A variable that is declared with static keyword is called static variable.

If you call this function many times, local variable will print the same value for each function call e.g, 11,11,11 and so on. But static variable will print the incremented value in each function call e.g. 11, 12, 13 and so on.


Automatic Variable

All variables in C that is declared inside the block, are automatic variables by default. By we can explicitly declare automatic variable using auto keyword.


External Variable

We can share a variable in multiple C source files by using external variable. To declare a external variable, you need to use extern keyword.