Dept. of CSE 1

Constants, Variables and Data Types

Md. Asif IqbalDaffodil International University

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Dept. of CSE 2

Character Set

A defined list of characters recognized by the computer hardware and software. Each character is represented by a number.

The ASCII character set, for example, uses the numbers 0 through 127 to represent all English characters as well as special control characters

The characters that can be used to form words, numbers and expressions those are to be used in C language.

The Character in C is grouped into following categories. Letters Digits Special Characters White Space Characters

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Dept. of CSE 3

Character Set…

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Dept. of CSE 4

C Token

In C Program the smallest individual unit is known as C Token.

C tokens are the basic buildings blocks in C language which are constructed together to write a C program.

Each and every smallest individual units in a C program are known as C tokens.

C tokens are of six types.

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Dept. of CSE 5

Keywords Keywords are those words whose meaning is already defined by Compiler Cannot be used as Variable Name C Keywords are also called as Reserved words . As C is a case sensitive language, all the keywords are written in lower case

letters. There are 32 Keywords in C:

auto double int structbreak else long switch

case enum register typedef

char extern return union

continue for signed void

do if static while

default goto sizeof volatile

const float short unsigned

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Dept. of CSE 6

Identifiers

In C language identifiers are the names given to variables, constants, functions and user-define data. These identifier are defined against a set of rules.

Rules for an Identifier An Identifier can only have alphanumeric characters( a-z , A-Z , 0-9 ) and

underscore( _ ). The first character of an identifier can only contain alphabet( a-z , A-Z ) or

underscore ( _ ). Identifiers are also case sensitive in C. For example name and Name are two

different identifier in C. Keywords are not allowed to be used as Identifiers. No special characters, such as semicolon, period, whitespaces, slash or comma

are permitted to be used in or as Identifier.

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Dept. of CSE 7

Constants

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

C supports several type of constants see the primary constants as below.

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Dept. of CSE 8

Constants…

1. Integer Constants: An integer constant refers to a sequence of digits. It contains of set of digits,0 to 9, preceded by optional - or + sign. It must be have a decimal point. valid example: 123 ,  -12  ,  0  ,  +78  ,  654321 Invalid: 15 750 ,  20,550  ,  $1232.Real constants:  A real constants refer to a sequence of digits the point. Number containing fractional parts like 15.55 such number are called

real(or floating) constants. Valid e.g. 0.0043, -0.75, +132.0 Invalid: 15.750 ,  20,550.33 ,  +$132

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Dept. of CSE 9

Constants…

3.Single Character constants:

A single character constant contain a single character enclosed within a pair of single quote marks. Each character constant represents an integer value. e.g :  '5'  ,   'x'  ,   ';'  ,  ' ' Note that the character constant '5' is not the same as number 5. The last constant is a blank space. character constants have integer value knows as ASCII (American code for

information interchange) values         printf("%d",'a');       I will print the number 97, the ASCII value of the letter a.

 printf("%d",97);        It will print the letter 'a'.

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Dept. of CSE 10

Constants…

String Constant: String is “Sequence of Characters“. String Constant is written in Pair of Double Quotes. String is declared as Array of Characters. In C , String data type is not available. Single Character String Does not have Equivalent Integer Value i.e ASCII Value

Different Constant Values Contained inside String :

Note: 'A' is not Equal to "A"

'A' ==> Requires 1 byte Memory "A" ==> Requires 2 byte Mem-

ory

Example Meaning

“a” String with Single Character

“Ali” String With Multiple Characters

“123? String With Digits

“How are You” String With Blanks

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Dept. of CSE 11

VariableVariables in C have the same meaning as variables in algebra. A variable in C is a storage unit, which sets a space in memory to hold a value and can take different values at different times during program execution.

Rules to construct a valid variable name Characters Allowed :

Underscore(_) Capital Letters ( A – Z ) Small Letters ( a – z ) Digits ( 0 – 9 )

Blanks & Commas are not allowed No Special Symbols other than underscore(_) are allowed First Character should be alphabet or Underscore Variable name Should not be Reserved Word

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Dept. of CSE 12

Case Sensitivity C is case sensitive

It matters whether an identifier, such as a variable name, is uppercase or lowercase.

Example:areaAreaAREAArEa

are all seen as different variables by the compiler.

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Dept. of CSE 13

Which Are Legal Identifiers?

AREA area_under_the_curve 3D num45 Last-Chance #values x_yt3 pi num$ %done lucky***

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Dept. of CSE 14

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 meatballs ; float area ;

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Dept. of CSE 15

Declaring Variables…

When we declare a variable Space is set aside in memory to hold a value of the specified data

type That space is associated with the variable name That space is associated with a unique address

Visualization of the declaration int meatballs ;

meatballs

FE07

garbage

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Dept. of CSE 16

Declaring Variables

Declaration of variables must be done before they are used in the program. Declaration does two things: It tells the compiler what the variable name is. It specifies what type of data the variable will hold.

#include<stdio.h>#include<conio.h>void main(){ int a,b,sum; //variable declaraction a=10; b=20; sum=a+b; printf("Sum is %d",sum); getch();}

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Dept. of CSE 17

"Data type can be defined as the type of data of variable or constant store.“

When we use a variable in a program then we have to mention the type of data. This can be handled using data type in C.

Followings are the most commonly used data types in C.

Data Types

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Dept. of CSE 18

Primary Data Types

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Dept. of CSE 19

Integer Types

Integers are whole numbers with a range of values supported by a particular machine.

There are signed integer and unsigned integer. Signed integer uses one bit for sign and other bits for magnitude of the number. Unsigned integers are always positive. It does not contain any bit for sign so that it occupies all the bit for the magnitude of the number.

By using equation -2^n to +(2^n)-1 we can find out the range of the number. Where n is the number of bits.

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Dept. of CSE 20

Size and Range of Integer Data

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Dept. of CSE 21

Floating Point Types

Floating point numbers are stored in 32 bits with 6 digits of precision.

Floating point numbers are defined in C by the keyword float.

When the accuracy provided by float is not sufficient double data type is used. It uses 64 bits giving a precision of 14 digits.

When you want to extend more precision you can use the long double data type. It uses 80 bits

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Dept. of CSE 22

Size and Range of Floating Point Data

Type Size(Bits) Range

float 32 3.4E-38 to 3.4E+38

double 64 1.7E-308 to 1.7E+308

long double 80 3.4E-4932 to 1.1E+4932

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Dept. of CSE 23

Void Types

Void type has no values.Void type does not return any values.These are used to specify the return

values from the function when they don’t have any value to return

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Dept. of CSE 24

Character Types

Character types data in C are defined by keyword char.

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Dept. of CSE 25

Typedef

Using typedef keyword we can define our own user defined data type.

Syntax:typedef type identifier;

Example:typedef int marks;marks sub1,sub2;

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Dept. of CSE 26

Enumeration

Declare using keyword enum Syntax: enum identifier {value1, value2, value3,….,valueN};

Example:enum day {Monday, Tuesday,……..,Sunday};

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