Variables in C

Variable is a name of the memory location which store data in variable whose value can be changed at the execution time of program.

int a=20; 
float f=20.8;
char c='A';

Some Rules for defining variables

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

Valid variable names:

int a;
int _ab;
int a30;

Invalid variable names:

int 2;
int a b;
int long;

There are Five types of variables in c:

Local Variable that is declared inside the function or block.

It must be declared at the start of the block.

You must initialize the local variable before .

void function1(){
int x=5;//local variable
}

Global Variable that is declared outside the function or block. Any function can change the value of the global variable.

Global Variable declared at the start of the block.

int value=20;//global variable
void function1(){
int x=10;//local variable
}

Static Variable that is declared with the static keyword..

void function1(){
int x=10;//local variable
static int y=10;//static variable
x=x+1;
y=y+1;
printf("%d,%d",x,y);
}

Automatic Variable explicitly declare an automatic variable using auto keyword.

 void main(){
int x=10;//local variable (also automatic)
auto int y=20;//automatic variable
}

You need to use extern keyword.It is flow the global globa

myfile.h

program1.c

#include "myfile.h"
#include <stdio.h>
void printValue(){
    printf("Global variable: %d", global_variable);
}