Introduction to C

INTRODUCTION TO C

Brief History of C

• The C programming language is a structure oriented programming language, developed at Bell Laboratories in 1972 by Dennis Ritchie.
• C programming language features were derived from an earlier language called “B” (Basic Combined Programming Language – BCPL)
• C language was invented for implementing UNIX operating system.
• In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C Programming Language” and is commonly known as K&R C.
• In 1983, the American National Standards Institute (ANSI) established a committee to provide a modern, comprehensive definition of C. The resulting definition, the ANSI standard, or “ANSI C”, was completed late 1988.
• Many of C’s ideas & principles were derived from the earlier language B, thereby naming this new language “C”.

Document Section

Links Section (File)

Definition Section

Global variable declaration Section

main() function definition

{

Variable declaration section

Function declaration section

executable statements;

}

Function definition 1

Function definition n

Simple C Program:

/* A simple program*/                     /*Document Section */

#include<stdio.h>                              /*Links Section (File) */

 #define pi 3.14                                  /*Definition Section */

main()                                                 /*main() fun. Definition */

{

int x=5;                                                /*Variable declaration section */

printf(“Hello student”);                    /*executable statements */

printf(“Value of a=%d”,x);

getch();

}

Stepwise explanation:

#include 

• The part of the compiler which actually gets your program from the source file is called the the preprocessor.
• #include <stdio.h>
• #include is a pre-processor It is not really part of our program, but instead it is an instruction to the compiler to make it do something. It tells the C compiler to include the contents of a file (in this case the system file called stdio.h).
• The compiler knows it is a system file, and therefore must be looked for in a special place, by the fact that the filename is enclosed in <> characters

<stdio.h> 

• h is the name of the standard library definition file for all STanDard Input and Output functions.
• Your program will almost certainly want to send information to the screen and read things from the keyboard, and stdio.h is the name of the file in which the functions that we want to use are
• The function we want to use is called printf. The actual code of printf will be tied in later by the linker.
• The “.h” portion of the filename is the language extension, which denotes an include

void

• This literally means that this means nothing. In this case, it is referring to the function whose name follows.
• Void tells to C compiler that a given entity has no meaning, and produces no error.

main

• In this particular example, the only function in the program is called main.
• A C program is typically made up of large number of Each of these is given a name by the programmer and they refer to each other as the program runs.
• C regards the name main as a special case and will run this function first e. the program execution starts from main.

(void)

• This is a pair of brackets enclosing the keyword void.
• It tells the compiler that the function main has no
• A parameter to a function gives the function something to work on.

{ (Brace)

• This is a brace (or curly bracket). As the name implies, braces come in packs of two – for every open brace there must be a matching close one.
• Braces allow us to group pieces of program together, often called a
• A block can contain the declaration of variable used within it, followed by a sequence of program
• In this case the braces enclose the working parts of the function

; (semicolon)

• The semicolon marks the end of the list of variable names, and also the end of that declaration
• All statements in C programs are separated by “;” (semicolon)
• The “;” character is actually very It tells the compiler where a given statement ends.
• If the compiler does not find one of these characters where it expects to see one, then it will produce an error.

scanf 

• In other programming languages, the printing and reading functions are a part of the
• In C this is not the case; instead they are defined as standard functions which are part of the language specification, but are not a part of the language
• The standard input/output library contains a number of functions for formatted data transfer; the two we are going to use are scanf (scan formatted) and printf (print formatted).

printf 

• The printf function is the opposite of
• It takes text and values from within the program and sends it out onto the
• Just like scanf, it is common to all versions of C and just like scanf, it is described in the system file stdio.h.
• The first parameter to a printf is the format string, which contains text, value descriptions and formatting

FILES USED IN A C PROGRAM

• Source File– This file contains the source code of the program. The file extension of any c file is .c. The file contains C source code that defines the main function & maybe other
• Header File– A header file is a file with extension .h which contains the C function declarations and macro definitions and to be shared between several source files.
• Object File- An object file is a file containing object code, with an extension .o, meaning relocatable format machine code that is usually not directly executable. Object files are produced by an assembler, compiler, or other language translator, and used as input to the linker, which in turn typically generates an executable or library by combining parts of object
• Executable File- The binary executable file is generated by the linker. The linker links the various object files to produce a binary file that can be directly

Running a C Program

• Type a program
• Save it
• Compile the program – This will generate an exe file (executable)
• Run the program (Actually the exe created out of compilation will run and not the .c file)
• In different compiler we have different option forcompiling and running. We give only the concepts.

Compilation and Execution:

                As like most high-level languages, C also uses compiler to convert its  source code (files with the extension.c) to object code (files with the  extension.obj) and the object code will be link edited by the linker to form the  machine language also known as executable code (files with the extension.exe ).