CSC335-Chapter2

8/13/2019 CSC335-Chapter2

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(Chapter 2-Introduction to Abstract Data Types)

CSC-335

Data Structures and Algorithms

Instructor:Ahmad Reza Hadaegh

The content of this power point lecture has been originally

created by Christos Kolonis and modified byDr. Ahmad R Hadaegh


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Chapter Contents

2.1 A first look at ADTs and Implementations2.2 C++'s Simple Data Types

2.3 Programmer-Defined Data Types

2.4 Pointers


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Chapter Objectives

Distinguish between ADTs and implementations of ADTs Review C++'s simple data types & ADTs they model

See examples of how implementations of ADTs aresometimes insufficient

Look at simple mechanisms to define new data types Take a first look at pointers and pointer operations


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2.1 First Look at ADTs & Implementations

For a programming task we must identify The collection of data items

Basic operations to be performed on them

EX: the car example, its properties and its functions

Taken together (data items & operations)

are called an Abstract Data Type (ADT)

Implementation

Storage structures for the data items

Algorithms for the operations (functions)


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Two's Complement Representation

For nonnegative n:

Use ordinary base-two representation with leading(sign) bit 0

For n < 0

1) Find w-bit base-2 representation of |n|2) Complement each bit.

3) Add 1

----------------------------------------------------------------------------

Ex: 00001010 in 8-bits system is equal to 10 indecimal. Now to get -10, we flip every bit to get11110101 and add 1 to get 11110110 which is -10 inbinary


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Example:

881. 88 as a 16-bit base-two number

0000000001011000

2. Complement this bit string

11111111101001113. Add 1

1111111110101000WHY?


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Works well for arithmetic computations

5 +6:

0000000000000101

+11111111111110101111111111111111

What gets done to

the bits to give this

answer?


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Problems with Integer Representation

Limited Capacity

a finite number of bits An operation can produce a value that requires more bits

than maximum number allowed.

This is called overflow .

None of these is aperfectrepresentation of(mathematical) integers

Can only store a finite (sub)range of them.

See Demonstrations Figure 2.1 and Figure 2.2


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2.2 C++ Simple Data TypesCharacter Data

1 byte for ASCII, EBCDIC 2 bytes for Unicode (java)

or C++ wide character type

Operations ==, , etc. Using numeric code


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2.2 C++ Simple Data TypesBoolean Data

Values {false, true } Could be stored in bits, usually use a byte

Operations &&, ||, !

In C++ bool type

int (boolVal) evaluates to

0 if false

1 if true


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Typedefs Mechanism usable to create a new type

Give new name to existing type

Example:

typedef double real;

Now eitherdoubleorrealcan be used.


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Enumerations Mechanism for creating types whose literals are

identifiers

Each identifier associated with unique integer


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Also possible to specify explicit values to give theenumeratorsenum NumberBase { BINARY = 2,

OCTAL = 8,

DECIMAL = 10,

HEXADECIMAL = 16};


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2.4 Pointers

When regular variables aredeclared

Memory allocated for valueof specified type

Variable name associatedwith that memory location

Memory initialized withvalues provided (if any)

Fig. 2.3

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2.4 Pointers

Pointer Variables value stored is a memory address

Note sample program, Figure 2.4

Declares variables that can store intaddressesand doublevariables

Displays the addresses


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Basic Pointer Operations

Dereferencing and indirection

Pointer variable stores address of a location

Accessing contents of that location requiresdereferencing operator *

Note program exampleFigure 2.5


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Basic Pointer Operations Assignment

Pointer variables can be assigned the values of otherpointer variables bound to same type


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Consider *jPtr = 44;

Changes value that both pointers reference

Not good programming practice, hard to debug

Known as aliasing problem

*iPtriPtr = &j


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Comparison Relational operators used to compare two pointers

Must be bound to same type

Most common == and !=

The null address may be compared with any pointervariable


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Dynamic Memory Allocation

The newoperation Example

typede int* intPtr;intPtr p = new int;

X

X

X

intPtr p = new int;


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Pointer Arguments

Pointers can be passed as arguments tofunctions

This is logically equivalent to reference parameters

In fact, this is how early C++ compilers accomplishedreference parameters


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Pointer Examples

int i1; int i2;

int* iPtr1;

Int* iPtr2; double d1;

double d2;

double* dPtr1;

double* dPtr2;

dPtr1 = &d1 dPtr1 = d1;

iPtr1 = & d1;

iPtr2 = &i2;

iPtr1 = iPtr2;

dPtr1 = iPtr1;

*iPtr1 = 19

*dPtr1 = *iPtr1;

*dPtr2 = 20.67;

*iPtr2 = *dPtr2;

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