Variables In C

Variables are names given to memory locations of computer where data are stored. Locations of variables can contain integer, real or character data types.

How To Declare Variable?

type variable_name;

Variable can not be used, if it is not declared. Data types of variable is needed to be put before the identifier in c language.

Rules for defining variables

Variables can have alphabets, digits, and underscore.
Variables can start with the alphabet, and underscore only. It can’t start with a digit.
No whitespace is allowed within the variable name.
Variables must not be any reserved word or keyword, e.g. int, float, etc.

Types of Variables in C

local variable
global variable
static variable
automatic variable
external variable

Local Variable – It is used & declared inside the function/block.

#include <stdio.h>
void func() {
   int a = 5; // local variable
}
int main()
{
   func();
}

Global Variable – It is used & declared outside the function/block.

#include <stdio.h>
   int a = 5; // global variable
   void func() {
      printf("%d",a);
   }  
   int main()
   {
      func();
   }

Static Variable – It is a variable that retains its value between multiple function calls. Its value get updated each time after operation on it.

#include <stdio.h>
   void func(){ 
   static int a = 30;//static variable 
   a = a + 10; 
   printf("%d",a); 
   } 
   int main() {
    
     func();
     func();
     return 0;
   }

Automatic Variable – All variables in C language that are declared inside the block, are automatic variables by default.

You can also explicitly declare automatic variable using ‘auto’ keyword.

#include <stdio.h>
   void func()
   {
     int a=4; //local variable (default automatic) 
     auto int b=5; //automatic variable
   }
   int main() {
       func();
       return 0;
   }

External Variable – Variables which can be used in different C files. You can declare external variable using extern keyword.

file.h
  extern int a=5;//external variable
  prog_name.c
  #include "file.h"  
  #include <stdio.h>  
  void printValue(){  
  printf("%d", global_variable);
  }

Variables In C

Variables In C

Discussion