C PROGRAMMING

SEMESTER:- 2^nd semester

SUBJECT:-COMPUTER APPLICATION

PREPARED BY :- A.P. Mohanty

Dept. of Science & Humanities

Introduction

• C is a general purpose language which is very closely associated with UNIX for which it was developed in Bell Laboratories.
• Most of the programs of UNIX are written and run with the help of 'C'.
• Many of the important ideas of 'c' stem are from BCPL by Martin Richards.
• In 1972, Dennies Ritchie at Bell Laboratories wrote C Language which caused a revolution in computing world .
• From beginning C was intended to be useful for busy programmers to get things done easily because C is powerful,dominant and supple language.

Why Name 'C' was given to this

language?

• Many of the ideas of C language were derived and taken from 'B' language.
• BCPL and CPL are previous versions of 'B' language.
• As many features came from B it was named as 'C'.

ABOUT “C”

• C is a structured programming language
• C supports functions that enables easy maintainability of code, by

breaking large file into smaller modules

• Comments in C provides easy readability
• C is a powerful language.
• C programs built from
• Variable and type declarations
• Functions
• Statements
• Expressions

- Structured and disciplined approach to

• C programming language

program design.

Structure Of “C” Programs

• Before going and reading the structure of C programs we need to have a basic knowledge of the following:
• C's Character Set
• C's Keywords
• The General Structure of a 'C' Program
• How To End A Statement
• Free Format Language
• Header Files & Library Functions

C's Character Set

C does not use every character set and key found on

modern computers . The only characters that C - Language uses for its programs are as follows:

​

• A-Z all alphabets
• a-z all alphabets
• 0-9
• # % & ! _ {} [] () $$$$ &&&& |
• space . , : ; ' $ "

✔ + - / * =

The keywords

• "Keywords" are words that have special meaning to the C compiler.
• Their meaning cannot be changed at any instance.
• Serve as basic building blocks for program statements.
• All keywords are written in only lowercase.

Basic Structure Of “C” Programs

#include<stdio.h> #include<conio.h>

void main()

{

-- other statements

}

Header Files

Indicates Starting of Program

Entry Point Of Program

Header files

• The files that are specified in the include section is called as Header File.
• These are precompiled files that has some functions defined in them.
• We can call those functions in our program by supplying parameters.
• Header file is given an extension .h .
• C Source file is given an extension .c .

Main function

• This is the “Entry Point” of a program.
• When a file is executed, the start point is the main function.
• From main function the flow goes as per the programmers choice.
• There may or may not be other functions written by user in a program.
• Main function is compulsory for any C program.

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 for compiling and running.

“C” language TOKENS

• The smallest individual units in a C program are known as tokens. In a C source program, the basic element recognized by the compiler is the "token." A token is source-program text that the compiler does not break down into component elements.
• C has 6 different types of tokens viz.

1. Keywords [e.g. float, int, while]
2. Identifiers [e.g. main, amount] 3. Constants [e.g. -25.6, 100]
4. Strings [e.g. “SMIT”, “year”]
5. Special Symbols [e.g. {, }, [, ] ]
6. Operators [e.g. +, -, *]

• C - programs are written using these tokens and the general syntax.

Strin gs

Keywords in Ansi “C”

The Identifiers

• They are programmer-chosen names to represent parts of the program: variables, functions, etc.
• Cannot use C keywords as identifiers
• Must begin with alpha character or _, followed by alpha, numeric, or _
• Upper- and lower-case characters are important (case-

sensitive)

• Must consist of only letters, digits or underscore ( _ ).
• Only first 31 characters are significant.
• Must NOT contain spaces ( ).

Constants

• Constants in C are the fixed values that do not change during the execution of a program.

CONSTANTS

Numeric constants

Character constants

Integer

Constants

Real Constants

Single Character

Constants

String

Constants

Constants Examples

• Integer Constants
• Refers to sequence of digits such as decimal integer, octal integer and hexadecimal integer.
• Some of the examples are 112, 0551, 56579u, 0X2 etc.
• Real Constants
• The floating point constants such as 0.0083, -0.78, +67.89 etc.

​

• Single Character Constants
• A single char const contains a single character enclosed within pair of single quotes [ ‘ ’ ]. For example, ‘8’, ‘a’ , ‘i’ etc.
• String Constants
• A string constant is a sequence of characters enclosed in double quotes [ “ ” ]; For example, “0211”, “Stack Overflow” etc.

DECLARATIONS

• Constants and variables must be declared before they can be used.
• A constant declaration specifies the type, the name and the value of the constant.
• any attempt to alter the value of a variable defined
• as constant results in an error message by the compiler
• A variable declaration specifies the type, the

name and possibly the initial value of the

variable.

​

• When you declare a constant or a variable, the compiler:

​

• Reserves a memory location in which to store the value of the constant or variable.
• Associates the name of the constant or variable with the memory location.

What Are Variables in C?

• A Variable is a data name that is used to store any data value.
• Variables are used to store values that can be changed during the program execution.
• Variables in C have the same meaning as variables in algebra. That is, they represent some unknown, or variable, value.

​

x = a + b

z + 2 = 3(y - 5)

• Remember that variables in algebra are represented by a single alphabetic character.

Naming Variables

• Variables in C may be given representations containing multiple characters. But there are rules for these representations.
• Variable names in C :
• May only consist of letters, digits, and underscores
• May be as long as you like, but only the first 31 characters are significant
• May not begin with a number
• May not be a C reserved word (keyword)
• Should start with a letter or an underscore(_)
• Can contain letters, numbers or underscore.
• No other special characters are allowed including space.

Case Sensitivity

• C is a case sensitive language.
• It matters whether an identifier, such as a variable name, is uppercase or lowercase.
• Example:

area Area AREA

ArEa

are all seen as different variables by the compiler.

Declaring Variables

• Before using a variable, you must give the compiler some information about the variable; i.e., you must declare it.
• The declaration statement includes the data type of the

variable.

• Examples of variable declarations: int length ;

float area ;

• Variables are not automatically initialized. For example, after declaration

int sum;

the value of the variable sum can be anything (garbage).

• Thus, it is good practice to initialize variables when they are

declared.

• Once a value has been placed in a variable it stays there until the program alters it.

Data types in ‘ansi c’

• There are three classes of data types here::

​

• Primitive data types
• int, float, double, char
• Aggregate OR derived data types
• Arrays come under this category
• Arrays can contain collection of int or float or char or double data
• User defined data types
• Structures and enum fall under this category.

Data Types- different attributes

Example of “C” Program

/* HELLO.C -- Hello, world */

#include <stdio.h> Void main()

{

printf("Hello, world\n");

​

Getch();

}