Basic of c programming and Variables

 

C Language Introduction

        C is a procedural programming language. It was initially developed by Dennis Ritchie in the year 1972. It was mainly developed as a system programming language to write an operating system. 

The main features of C language include low-level access to memory, a simple set of keywords, and clean style, these features make C language suitable for system programmings like an operating system or compiler development.
Many later languages have borrowed syntax/features directly or indirectly from C language.

 Like syntax of Java, PHP, JavaScript, and many other languages are mainly based on C language. C++ is nearly a super set of C language (There are few programs that may compile in C, but not in C++).

Types of applications:-

1. Standalone Applications

2. Web Applications

1.Standalone Applications:-

• Must be installed (ex:- VLC player,ms- office,etc).

• Compatible for single -OS.

2. Web Applications:-

1. No need install (ex Gmail.com,Facebook.com,IRCTC.com etc).
2. Independent to OS.

Program  language is Standalone or Web Applications???

• all language  are standalone(installation is mandatory)

• C and c++ Language is platform dependent - create only standalone Applications

• Java,C#,etc platform independent -create  standalone Applications and Web Applications

Main things to write a C program

• Variables:-Program sharing is called variables

• Methods:-when two program want to communication what we are using is called method (also called as functions)

Variables:-

named memory location 

Ex:-Bank application 

Set identity  to location there wise variables store at random place and finding is default

that why set identity to location

Syntax:-

Data Type  Identities;

ex:- int a=2;

Rules for defining variables:-

• A variable can have alphabets, digits, and underscore.

• A 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.

• A variable name must not be any reserved word or keyword, e.g. int, float, etc.

Types of Variables in C:-

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 a local variable.

It must be declared at the start of the block.

void function1(){  

int x=10;//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 a global variable. Any function can change the value of the global variable. It is available to all the functions.

It must be declared at the start of the block.

int value=20;//global variable  

void function1(){  

int x=10;//local variable  

} 

Static Variable:-

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

It retains its value between multiple function calls.

void function1(){  

int x=10;//local variable  

static int y=10;//static variable  

x=x+1;  

y=y+1;  

printf("%d,%d",x,y);  

}  

If you call this function many times, the local variable will print the same value for each function call, e.g, 11,11,11 and so on. But the 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 are declared inside the block, are automatic variables by default. We can explicitly declare an automatic variable using auto keyword

void main()

{  

int x=10;//local variable (also automatic)  

auto int y=20;//automatic variable  

}  

External Variable:-

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

myfile.h

extern int x=10;//external variable (also global)  

program1.c

#include "myfile.h"  

#include <stdio.h>  

void printValue(){  

    printf("Global variable: %d", global_variable);