What is C language? (INTRODUCTION)
C is a general-purpose , high level  language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system ta Bell labs. C was originally first implemented on the DEC-PDP-11 Computer in 1972.
In  1978 , Brain Kernighan and Dennis Ritchie produced the first publicly available description of C, now known as the K&R standard.
The UNIX operating system, the C compiler, and essentially all UNIX application programs have been written in C.
C has now become a widely used professional language for various reasons-
  • Easy to learn 
  • Structured language
  •  It produces efficient programs . 
  • It can handle low-level activities
  •  It can be compiled on a variety of computer platforms .
Facts about C 
  • was invented to write an operating system called UNIX.
  • C  is a successor of B language which was introduced around the early 1970s.
  • The language was formalized in 1988 by the American National Standard Institute (ANSI).
  • The UNIX OS was totally written in C.
  • Today C is the most widely used and popular System Programming Language.
  • Most of the state-of-the-art software has been implemented using C.
  • Today's most popular Linux OS and RDBMS MySQL have been written in C .
Why use C
C was initially used for system development work, particularly the programs that make-up the operating system. C was adopted as a system development language because it produces code that runs nearly as fast as the code written in assembly language. Some examples of the use of C might be -
  • Operating Systems
  • Language Compilers
  • Assemblers .
  • Text Editors .
  • Print Spoolers
  • Network Drivers
  • Modern programs
  • Database
  • Language interpreters
  • Utilities
C Programs
A c program can vary from 3 lines to millions of line and it should be written into one or more text files with extension “.c”; for example, hello.c. You use “vi”, “vim” or any other text editor to write your C program into a file.
C program Structure
       Basically a C program involves the following section,
  • Documentations
  • Pre-processor Statements
  • Global Declarations
  • The main () function

                1. Local Declarations
                2. Program statements and Expressions

  • User defined Functions

Sample code of C “Hello World” program:
Example:
                #include<stdio.h>
                #include<conion.h>
                Void main()
{
     /*first C program*/
    Printf(“HELLO WORLD\n”);
           Return;
}

Or in different way
 #include<stdio.h>
int main()
{
     /*first C program */
  Printf(“HELLO, WORLD!\n”);
      Return 0;
}

Let’s look into various parts of the above C program
/*comments*/- : ( Comments are a way of explaning what makes a program. Comments are ignored by the compiler and used by other to understand the  code. )

"include<stdio.h> :  (stdio is standard for input/output, this allows us to use some commands which include s header file called stdio.h )

int/void main() : int/void is a return, which will be explained in a while.

main()  The main() : The main() is the main function where program execution begins. Every C program must contain only one main function.

Braces : Two curly brackets "{...}" are used to group all ststements together.

Printf() return 0 : Its is function in C, which prints text on the screen. At the end of the main function return value 0.
Basic Syntax of C
Semicolons :
                      In a C program, the semicolon is stastements terminator. That is, each individual statements must be ended with a semicolon. It indicates the end of one logical entiry.
Given below are two different statements-
printf("HELLO,WORLD!\n")
return 0;

Identifiers:
                    A C identiffier is a name uded to identify a variable, function, or any other user-defined item. An identiffier starts with A to Z, a to z an underscore '_' followed by  zero or more letters, underscore, and digits ( 0 to 9 ). C dose not allow punctuation characters suc as @, &, and % within identiffiers. C is a case-sensitive programming language. Thus, Manpower and manpower are two different identiffiers in C. Here are some examples of Accertable identiffiers-
    emp_name a_123
    myname50  _temp j a23b9 retVal


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