C Variables

Syntax of variables

type variable_list;

Example of some valid variable declaration

int    a,b;
char   c;
float  d,month;
double k,salary;

Syntax of variables

• A variable will have alphabets, digits, and underscore.
  Example: int _ab,a1,ab;
• No white area is allowed at intervals variable name.
  Example: int a b;
• A variable name will begin with alphabet and underscore solely.
  Example: int _ab;
• A variable name should not begin with the digit.
  Example: int 5;
• A variable name should not be any reserved word or keyword.
  Example: float, int and etc.

Types of variables

• Local variable
• Global variable
• Static variable
• Automatic variable
• External variable

Local variable

Local variables are used in within the function only, these variables won’t work outside of the function.

void function(){
	int a=10;	// Local variable
}

Global variable

Global variables are used in the entire program, these will work anywhere in the program. These variables are defined outside of the function.

int b=20;	// Global variable
void function(){
	int a=10;	// Local variable
}

Automatic Variable

Automatic Variable is asserted within the block. The automatic variable is the default variable. Automatic variables are explicitly declared auto keyword.

void main(){  
	int a=14;	//local variable (It is also automatic variable)  
	auto int b=12;	//automatic variable  
} 

External Variable

External Variable declared with extern keyword. when you declare extern keyword for the variable then it can access in one or more source file.

file.h
extern int x=10;	//external variable (also global)  
-------------------------------------------------------
#include "file.h"  
#include   
void printValue(){  
		printf("Global variable: %d", global_variable);  
}

Static Variable

Static Variable is declared with static keyword.

void function1(){  
	int a=10;	//local variable  
	static int b=10;	//static variable   
	printf("%d,%d",a,b); 
	b++; 
}

Environment variable

Environment variables are applicable for all the C applications and C programs. There are 3 functions which can be used for these variables: setenv( ), getenv( ) and putenv( ).