Introduction to C

• History of C
• Characteristics / Features
• Structure of a C Program
• Desirable Program Characteristics
• C Character Set
• Identifiers & Keyword
• Constants
• Expression
• Statements
• Symbolic Constants

History of C

• This language was developed by Dennis Ritchie in 1970 at t he Bell Lab.

• It was official released only in 1978.

• 1980s it evolved as a most effective language because of its desirable features.

• It was instantly adapted even for developing commercial applications

• Many Software products which were written in other languages we rewritten in C for its efficiency and portability.

• With the advent of C many C compilers and interpreters were written and released into the market

• They differed from the original C language this lead to the lack of portability that the language promised to provide

• AT this point ANSI developed certain standardized norms for the C language and today all C compilers adhere to this ANSI Standard.

Characteristics / Features

• Ability to write very concise source codes in spite of having a large number of operators.

• It has a small instruction set

• It has library functions that enhance the basic instruction.

• The features and capabilities can be easily extended b the users as it encourages users to write additional library functions

• C Compliers are compact and generate smaller and highly efficient object code compared to other high level languages.

• C Programs are highly portable as its library set avoids all to computer dependent features.

• C Compliers are compact and generate smaller and highly efficient object code compared to other high level languages.

• C Programs are highly portable as its library set avoids all to computer dependent features.

Structure of a C Program

CODE

/* Simple Program to Add 2 Values*/            /* Title*/[/color]
[color="#996633"]# Include<stdio.h>                        /*Library File Access*/
main()                                          /* Function Heading*/
{                                                  /* Start of the Function*/
    int n1,n2,sum;                          /* Variable Declaration*/
    printf(“Enter First Value : “);        /* Output Statement */
   scanf(“%d “,&n1);                       /* Input Statement */
   printf(“Enter Second Value : “);    /* Output Statement */
   scanf(“%d “,&n2);                       /* Input Statement */
   sum=n1+n2;                              /* Assignment Statement*/
   printf(“Sum is : %d “,sum);          /* Output Statement */
}                                                  /* End of function Main*/

Desirable Program Characteristics

• Integrity
• Clarity
• Simplicity
• Efficiency
• Modularity
• Generality

C Character Set

• Uppercase A - Z
• Lowercase a - z
• Digits 0 – 9
• Special characters

These are used as building blocks to form basic program elements


Identifiers & Keyword

Names given to basic program elements such as variables, Functions etc. Certain norms they have to follow:

• Name can be of alphanumeric type
• But should start with a alphabet
• It is case sensitive
• Keywords are reserved words that have a predefined function in C
  
• Keywords can be used only for the purpose they are intended for
  
• Keywords Cannot be used as program defined identifiers

Constants

They contain a specific value.
Four types :

Integer & Floating Point Constants

They are normally reffered to as numeric constants
Follow certain norms:

• Commas and blanks cannot be included within the constant
• Can be preceded with a – sign if required
• Value should be within the specified range .

Integer Constants

These are nothing but integer valued numbers.
Can be written in 3 number systems :

• Decimal Integer Constant ( Base 10)

Contains digits between the set 0 to 9
If consists of more than one digit should start with a value other than zero.

• Octal Integer Constant ( Base 8)

Contains digits between 0 to 7
First digit must be a zero

• Hexa Integer Constant (Base 16)

Begins with a either 0x or 0X followed by digits
Set could contain 0 to 9 and a – f (Lower or Uppercase)

Floating Point Constants

• This is a base 10 number having a decimal value or a exponent.

• In case of representation of a exponent is similar to the scientific notation except that 10 is replaced by E or e

Eg : 10.8X 10 -3 : 10.8E-3 or 10.8e-3

Character Constants

• Single character enclosed within Single apostrophes

• All character constants have integer values that determine them in the character set .

• Character set standardized by the ASCII here each character is numerically encoded with its own unoaque 7 bit coding

Combination of special characters that are used for special purpose .
Always started off with a \ .
Eg \n, \t etc.

String Constant

• Consecutive sequence of characters within double quotations.
• Uses \0 ( Null) string terminator at the end of the string.

Expression

• Represents a single data item which could be a number or character .
• It could be single entity as a variable function or constant or a combination of entities connected by a operator.

Eg. C=a+b;


Statement

This Causes the computer to perform a action
Types:

• Expression Statement
• Compound Statement
• Control Statements.

Symbolic Constant

• Name that substitutes with a sequence of characters.

• These sequence of characters could represent a numeric , character or a string constant.

• They have to be defined at the beginning of the program

• Done by using the keyword : # define pi 3.141

, in the next tutorial. Suggestions and Critisizm are welcome ..

Regards
Dhanesh.