CS112 Intro to CS II with C++

Introduction

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Problems and Programs

Program helps articulate structure of Problem, and maybe even solve it“Model the World”Hence “objects”Functional spec

What

Design specHow

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“Your world”

cin cout

var x

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“Your world”: example (p.4)

cin cout

var x var yvar su

m

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“Your world”: Primitive Objects“Built-in”:

Numbers int; long; float; double

CharactersOperators:

+; -; /; *“boxes”: variablesStreams: I/O

cin; coutBring them in: Libraries

#include <stdio.h>; … <iostream.h>;…

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“Your world”: Creation - new from old

Combining Objects“Simple glue”:

arraysstruct

expressions

Objects from objects:classes

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“Your world”: Creation ‘ex nihilo’

ConstructorsCreate objects of defined kind (class)

DestructorsClean up after yourself – remove the objects you createdOtherwise: Memory leaks

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Example

Example from G:pg.4On blackboard

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Objects: from Outside and Inside

Top-down approachFrom outside: Interface

Define/design interfaces first and wellInterface defines the objectInterface and its use makes no assumptions about implementation of object

From Inside: Object implementationDepends only on interface, not on how the object will be used

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Independence and Structure

Easy maintenanceIf object implementation changes (without change of interface) the rest of the program will continue to workObjects can be re-used in ways not originally anticipated (as long as interface is same)

Easy designClarity (“Pictorial”)

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Everything is an object (example)

Object: operator “+”Integer addition

In:int a, b

Out:int c=a+b

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Implementation oblivious

You can use “+” without knowing how it is implemented!

E.g. suppose it was implemented as repetitive incrementing (the way children count on their fingers)When a new implementation based on grade school arithmetic is developed you see only speed improvement

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Continued example – extending

Real numbers addition

In:Float x, y

Out:Float z=x+y

Looks simple…

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Extending example further…

Character strings concatenation

In:string a, b

Out:string c= a||bc=a+b

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Another example – bottom up

Atomic objectsNumbers, characters, strings, etc.

Pair (in Lisp: CONS)Using Pair, build

Link-listStackTreeGraph

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Link-list

Link-list = Pair of an element and a (smaller) link-

list

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Link-list (cont.)

Recursive

Termination – nil-object

“Inside view”!

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Stack

Collection of elementsCan add, remove elementsLast in – first out (LIFO)

Interface (access methods):Push ( element e, Stack S )Pop ( Stack S ) element eEmpty? (Stack S ) bool empty

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Stack implementation

Link-list Empty? ( S ) : S = Push (e, S): S Pair (e, S)Pop (S):

Let S = Pair (x, S¯)Set S S¯; Return x

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Life of a Stack

Pop

Push (3 boxes)

Create empty stack (!!!)

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StackCollection of elements

Can add, remove elementsLast in – first out (LIFO)

Interface (access methods):Push ( element e, Stack S )Pop ( Stack S ) element eEmpty? (Stack S ) bool empty

Create empty stack

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Simple List

Interface:Create empty listInsert elementsDelete elementsEmpty?

More complex…Concatenate lists, split, etc.

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Tree

Binary Tree = Pair ( left sub-tree, right sub-tree )

Internal structure

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Graph

Graph = List of nodesNode = Pair (node info;

List of adjacent nodes)

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Generic object

Object = Pair ( ID, List of attribute-value

pairs )Example

Instructor = (bu.cas.cs112.a1.2003.fall, ( (name, “Gene Itkis”), (phone, 353-5285), (office, mcs284), (course, cs112), … ) )

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In and out once againImplementation techniques vs. Objects/Data StructuresObjects & Data Structures

Clear interfaceHidden implementation detailsExamples: Stack, Simple List

Implementation techniquesExamples: Link-list, Tree, Graph, Generic Object

Object from one perspective can be an implementation detail from another