Elements of C

Contents

• —How C program gets executed
• —C Tokens
• —Variables
• —Primary Data Types

How the program gets executed

• —Enter the program using any editor
• —Edit the source program
• —Compile the code
• —If syntax error exists then edit the program again
• —If syntax error does not exist then Object code is created (filename.obj)
• —Execute the Object code and check input data
• —The code check for errors
• —If Logic error exists then edit the program
• —If Data error exists input data is again given to the program
• —If code is error free then output appears on screen

•In a passage individual words and punctuation marks are  called as tokens
•In C individual units are called Tokens

32 Keywords in C!!

• —Keywords are words whose meaning is already explained to C Compiler
• —Must be written in lowercase letters

Identifiers!!

—Identifiers  are user-defined words and is used to give names to entities like

• —Variables
• —Arrays
• —Functions
• —Structures

Rules for Naming Identifiers

—The name should consist of only

—Alphabets (A,B…..Z or a,b……z)

—Digits (0,1…..9)

—Underscore sign (_)

—First character should be an alphabet or underscore

—The name should not be a keyword

—Code, code and CODE are three different identifiers

—Length

• —Some compilers recognize 31 characters 

Constants

• —Constants is a value that do not change during the execution of a program

Integer Constants

• —Integer constants refers to sequence of digits

• —Three types of integer constants

• —Decimal (base 10)
• —Octal  (base 8)
• —Hexadecimal (base 16)

Rules for Integer Constants

• —Must have at-least one digit

• —Must not have a decimal (.) point

• —Can be either +ve or –ve

• —No commas or blanks are allowed

• —Allowable range is -32768 to 32767 for 16 bit compiler

—Ex:

Real Constant

—Also known as floating point constants

—Contains decimal point

—Two forms of real constants

1. —Fractional
2. —Exponential

Rules for Fractional Form

• —Must have atleast one digit
• —Have a decimal point
• —Either +ve or –ve
• —No commas or blanks are allowed
• —Ex:

Rules for Exponential Form

—The constant is divided into two parts

• —The part appearing before e is called mantissa
• —The part following e is called exponent

—

The mantissa and exponent is separated by letter e

——Mantissa may have +ve or –ve sign

—Exponent must have at-least one digit

—Exponent may have +ve or –ve

Character Constant

—Is a single alphabet, digit or special symbol enclosed within single inverted commas (‘’)

—Maximum length can be 1 character

—Ex

• —‘A’
• —‘1’
• —‘5’
• —‘$’

Backslash Character Constant

String Constant

—Sequence of characters enclosed in double quotes (“”)

—‘X’ ≠ “X”

—Ex

• —“Hello!”
• —“987”
• —“%% &*”
• —“5+4”

Special Symbols

—Also known as Delimiters

Operators

—Operator specifies an operation to be performed

Variables

—Variable is a name used to store values

—Values assigned to variable can be changed during execution of a program

Data Types

• —A type is a collection of values with shared properties
• —Using types makes a program easier to read and understand
• —Using types makes it easier for the compiler
• —Types makes it easier to detect certain programming errors

Classes of Data Types

• —Primary (Fundamental) Data Types—
• —User-defined Data Types—
• —Derived data types
• ——Empty Data set

Primary Data Types

Use of Qualifiers

Range of Data Types

Example

#include<stdio.h>

main()

{

   int a, b, c, d;        //declaration

   unsigned u = 10;       //declaration

   a = 12; b = -24;       //assignment

   c = a + u; d = b + u;  //assignment

   printf(“a+u=%d, b+u=%d\n”, c, d);

}

output:

a+u=22, b+u=-14

See you in the next post.....