What is C language - Structure and syntax of C language

C is a general-purpose, high-level language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system at 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 Language 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 

• 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 lines 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
• Local Declarations
• Program statements and Expressions
• User-defined Functions

Sample code of C “Hello World” program:-

#include
#include

Void Main()
 {
   /*first C program */
Print("Hello World")
     Return;
}

Program Output:

Hello World!
_

Or in different way:

#include
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 explaining what makes a program. Comments are ignored by the compiler and used by others 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 statements together.

Printf() return 0: It is a 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 a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

Given below are two different statements:-

printf("HELLO,WORLD!\n")

return 0;

Identifiers:

A "C" identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with A to Z, a to z an underscore '_' followed by zero or more letters, underscores, and digits ( 0 to 9 ). C does not allow punctuation characters such as @, &, and % within identifiers. C is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C. 

Here are some examples of Acceptable identifiers:-

    emp_name a_123

    myname50  _temp j a23b9 retVal