chapter 5 data type

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CMPF134: Fundamentalsof Data and Information

Chapter 5Data Types

1



Learning Objectives

To be exposed to the different type of dataused in programming.

To be able to differentiate the characteristicsof each data type.

To be able to give examples of each datatype

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Introduction

It is easy for humans to distinguishbetween different types of data.

We can usually tell at a glance whether anumber is a percentage, a time, or an

amount of money. However, we need to define data type in

computing system because the data type

defines: the amount of storage allocated to variables.

the values that they can accept.

the operations that can be performed on

variables. 3



Basic Data Types

FIVE common data types include: Integers

Boolean

characters floating-point numbers

alphanumeric strings.

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Integer

An integer is typically specified in theprogram as a sequence of digits,without spaces or thousands

separators, optionally prefixed with +or -.

It is also what commonly we refer as

the whole number. Some programming languages allow

alternative notations, i.e hexadecimal(base 16) or octal (base 8).

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Examples

Valid integer values 1009

321

9999999 Invalid integer values:

1,009

321.0 $999999

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Integer sizes

In math natural number are 0, 1, 2,….. and the list goes on infinitely.

In a machine only a finite portion of

these numbers can be representedand it will depend on the size of memory allocated for that number.

Commonly (and it may varies in lowerand higher end computers) an integerwhen declared in a program will beallocated a size of 4 bytes – 32 bits.

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Range of integer values

The maximum (Max_int) and minimum (Min_int)value of an integer will depend on the number of bits (n) that is allocated for it.

Max_int = 2n-1 -1

Min_int = - 2n-1

For a 32 bits (4 bytes) sized word:

Max_int = 231 -1 = +2147483647

Min_int = - 231 = -2147483648

So all integer variable (e.g. x) should carry thevalue of : Max_int ≥ x ≥ min_int, if not we willhave an error called overflow (value too large) orunderflow (value too small).

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Examples

On machine with 2-byte word length(16 bits)

Max_int = +32767

Min_int = -32768

What would be the maximum and

minimum value of an integer if wehave a word size of 8 bits?

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Boolean (cont)

Comparison operators return a Boolean valueindicating the truthfulness of the expression.

Operators(symbol)

<

<=

>

>=

==!=

<>



Boolean (cont)

2 < 4True

2 == 4

False2 > 4

False

6.2 <= 6.2True

6.2 <= 6.20001

True



Boolean (cont)Operators

and

or

not

•

We can use conjunction operations to chain togetherarbitrary expressions and logically combine the Boolean

results:

2 < 4 and 2 == 4

False

2 > 4 or 2 < 4

True

not 6.2 <= 6

True



Boolean (cont)

3 < 4 < 5True

3 < 4 < 5 is a short way of saying3<4 and 4<5

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Example:

Selection control structure Compare two statements

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Character

Character fields or can store textinformation that is not used inmathematical calculations, such as

names, addresses, and numbers. For example, phone numbers or zip

codes, though they include mostly

numbers, are actually best stored ascharacter values.

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Character (cont)

A single character data is usually written inprograms with a single quote e.g. „a‟, „D‟,

„5‟, „&‟ etc.

It can be any digit, blank space,

punctuation mark, etc

Each of the character will be represented inthe computer as a numerical value based

on the type of encoding it use (nextchapter topic).

Example of ASCII code table is provided asbelow:

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ASCII d t bl F t f



ASCII codes table - Format of standard characters

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ASCII d t bl F t f



ASCII codes table - Format of standard characters (cont)

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ASCII d t bl F t f




22

ASCII d t bl F t f




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ASCII d t bl F t f




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Character (cont)

Character or char „6‟

„L‟

„*‟

„m‟

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Alphanumeric String

A string is a sequence of symbols thatare chosen from a set of alphabet,number or blank space, punctuation

mark, etc A string will contain more than one

character and are usually written withdouble quotes, e.g. “Hello there ..123”

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Examples

Strings “CMPF134”

“$123.00”

“I love studying in Uniten”

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Floating point

Floating point describes a system for representingreal numbers which supports a wide range of values.

Numbers are in general represented approximatelyto a fixed number of significant digits and scaledusing an exponent. Significant digits × base exponent , in the scientific notation form.

E.g. 934.5678 can be represented as

9.345678 x 102

(since the actual decimal point has been moved to theleft 2 positions, and the exponent is based 10 as thenumber is in base 10 (decimal numbering system))

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Floating point (cont)

The term floating point refers to the factthat the radix point (decimal point) can"float"; that is, it can be placed anywhererelative to the significant digits of the

number. This position is indicated separately in the

internal representation, and floating-pointrepresentation can thus be thought of as acomputer realization of scientific notation.

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Floating point (cont)

the most commonly encountered representation isthat defined by the IEEE 754 Standard. (you willlearn of this internal representation of a floatingpoint number in your degree course)

In our programs we may write floating pointnumbers as we usually do for real numbers e.g.

569.001, 0.6780 etc. (no need in scientific notation)

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Example

Floating point numbers: 12.55

569.001

0.6780 934.5678

9.345678 x 102

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chapter 5 data type

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