C Tutorial

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Variable in C

Variable is an identifier that holds data in memory. It is used to identify input data in a program. The value of the variable can change at the time of executions. Let’s consider the syntax of a variable.

Syntax: Datatype variable_name;
Syntax: Datatype  variable_name1, variable_name2,variable_name3…variable nameN.
We can also declare multiple variables with the same data type by using comma (,). Example:
int a, b; // a and b are variable and int is the data type.
char c; // c is a variable and char is the data type.
Rules for declaring the variable:
  • Variable name should start with alphabets or underscore (_).
  • No space is allowed in a variable while declaration.
  • Variable must not be any reserved word or keyword.
Let’s see some example of how to declare the variables.
Valid declaration  Invalid  declaration
int  b; int 2;
char _name; int  a b;
int a4; int  double;

Types of variables in C.
There are various types of variable in C:
  1. local variable
  2. global variable
  3. static variable
  4. automatic variable
  5. external variable
1. Local variable: A local variable is declared inside of the function or block. It must be declared at the start of the block. Example:
void function1()
float x= 34.9; // Here x is local variable.
2. Global variable A global variable is declared outside of the function or block. The value of the global variable can be changed.
char name=”ABC”; // global variable
void function1()
int x=10; // local variable
3. Static variable A static variable is declared with the static keyword. It contains its value during the function call. Example:
void function1(){
int x=5;//local variable will print the same value.
static int y=5; //static variable will print the incremented value like: 5,6,7,...N
4. Automatic variable An automatic variable is declared inside the block. The auto keyword is used to declare the automatic variables.
void main()
int a=5;// Here a is local variable or also automatic variable.
auto int b=10;//automatic variable
5. External variable An external variable is used to share the multiple C source files by using external variables // save it as abc.h
extern int x=5;  //external variable (also global)
//save as prog1.c
#include "myfile.h"
#include <stdio.h>
void printValue()
printf("Global variable: %d", global_variable);