IntroductionSoftware Engineering with OOP

Software Crisis

Common software systems behavior Does not provide required functionality Is over budget with respect to time and money and computer

resource usage Not adaptable to changing user needs

Why? User needs are ill-specified Complexity of interactions grows multiplicatively Human cooperation limits Programming is difficult

Software Engineering

Goal Ease the development of reliable, flexible,

economical software Techniques

Group management Complexity management Measuring software quality

Caveat Throwing more people at a problem isn’t always the

best way to fix it

Software Development Basics

System Design What is the solution?

Program DesignWhat are the mechanismsthat best implement thesolution?

Program ImplementationHow is the solutionconstructed?

Testing Is the problem solved?

Delivery Can the customer use the solution?

Maintenance Are enhancements needed?

ProblemDomain

ProblemDomain

ImplementationDomain

ImplementationDomain

Over 50% of development costs!

Requirements Analysis What is the problem?

Specifications Problem statement for programmers

C++ Designer

Stroustrup Purpose

To implement software tools more quickly, reliably, and economically

Principal features Implements most of C (superset) Supports object-oriented programming Reusable software components that have both

attributes and behavior — i.e., objects

Where Do We Go From Here? Machine organization, programming, translation software, programming

environments, data representations, terminology, history, software engineering, object-oriented design [1]

C++ fundamentals, C++ programs, C++ objects, input, output [2] Modifying objects, arithmetic, operator precedence, strings [3] Control constructs, Boolean objects, programming logic, conditional

execution, switch statement [4.1-4.5] Repetition, looping, for and while and do loops [4.6-4.12] Functions, library programs: iostream, iomanip, fstream, generating and

using random numbers [5] Programmer-defined functions, parameters, pass by value, pass by

reference [6] Classes: programmer-defined data types, constructors, object-oriented

design and analysis [7] Inheritance [8]

A C++ Program// Canonical first program

#include <iostream>

#include <string>

using namespace std;

int main() {cout << "Hello world!" << endl;

return 0;

}

Pre-processor directives

A using directive

Software Engineering Goals

Reliability An unreliable life-critical system can be fatal

Understandability Future development is difficult if software is hard to

understandCost Effectiveness

Cost to develop and maintain should not exceed profitAdaptability

System that is adaptive is easier to alter and expandReusability

Improves reliability, maintainability, and profitability

Software Engineering with OOP Identity

Data are organized into (named) objects Abstraction

Extract the relevant properties while ignoring inessentials Divide an object into smaller modules (modularity) Simplify to make it easier to understand

Classification (Hierarchy) Ranking or ordering of objects based on some relationship

between them Encapsulation

Couple the data PLUS the operations on that data together; Also, hide and protect essential information (implementation details) behind a controlled interface – i.e., information hiding.

Inheritance Ability to create new classes based on existing ones

Polymorphism Exhibiting the same behaviour differently on different classes or

subclasses Persistence

Extract the relevant object properties while ignoring inessentials Defines a view of the object

Example - car Car dealer views a car from selling features standpoint

Price, length of warranty, color, … Mechanic views a car from systems maintenance standpoint

Size of the oil filter, type of spark plugs, … Driver views a car from usability standpoint

How fast does it go, fuel consumption, etc…

Abstraction

Price? Oil change?

Encapsulation Steps

Decompose an object into parts Data and Methods that operate on them go together

Hide and protect essential information (implementation details) Information Hiding is hiding implementation details; encapsulation (a

language construct) is not the same thing as information hiding (a design principle), although it implements it

Supply interface that allows information to be modified in a controlled and useful manner

Internal representation can be changed without affecting other system parts

Example - car radio Interface consists of controls

and power and antenna connectors The details of how it works is hidden To install and use a radio

Do not need to know anything about the radio’s electronics

Modularity

Dividing an object into smaller pieces or modules so that the object is easier to understand and manipulate

Most complex systems are modular

Example - Automobile can be decomposed into subsystems

Cooling system Radiator Thermostat Water pump

Maneuvering Steering Wheels Brakes

Ignition system Battery Starter Spark plugs

Hierarchy Hierarchy

Ranking or ordering of objects based on some relationship between them

Help us understand complex systems Example - a company hierarchy helps employees

understand the company and their positions within it

For complex systems, a useful way of ordering similar abstractions is a taxonomy from least general to most general

OO Design and Programming Object-oriented design and programming methodology

supports good software engineering

Promotes thinking in a way that models the way we think and interact with the real world

Example - watching television The remote is a physical object with

properties Weight, size, can send message

to the television The television is also a physical object

with various properties You are also a physical object

With eyes, ears, etc.

Objects An object is almost anything with the following

characteristics

Name (Identity)

Properties (data and function members)

The ability to act upon receiving a message Basic message types

• Directive to perform an action (function member)• Request to change one of its properties (mutator)• Request to get the value of one of its attributes

(accessor)

All you need is love objects?

Objects are implementations of Abstract Data Structures

But to make programs, we also need algorithms!

Algorithms + Data Structures = Programs Nicklaus Wirth (creator of Pascal)

What’s an Algorithm?

A predetermined series of instructions for carrying out a task in a finite number of steps I.e., Baking A Cake!

Two commonly used tools to help document the program logic (the algorithm): Flowcharts and Pseudocode.

Generally, Flowcharts work well for small problems but Pseudocode is used for larger problems

Flowchart: Symbolic Representation of Algorithms

Flowchart: A graphic representation of an algorithm, often used in the design phase of programming to work out the logical flow of a program

Some Control Structures Sequence Selection Repetition (Looping)

Pseudocode! What is pseudocode?

Pseudocode is basically short, English phrases used to explain specific tasks within a program's algorithm. Pseudocode should not include keywords in any specific computer languages. Indentation can be used to show the logic in pseudocode as well.

Why is pseudocode necessary? Writing pseudocode WILL save you time later during the construction & testing phase of a program's

development let’s you “think out” the program before you code it. How do I write pseudocode?

Consists mainly of executable statements

Original Program Specification: Write a program that obtains two integer numbers from the user. It will print out the sum of those numbers.

Variables required (names and types): int1: (integer) to store first integerint2: (integer) to store the second integersum: (integer) to store the sum of the numbers

Pseudocode: Prompt the user to enter the first integer int1Prompt the user to enter a second integer int2Compute the sum of the two user inputs sum = int1 + int2Display an output prompt that explains the answerDisplay the result

If you can’t write it in pseudocode, you won’t be able to write it in C++!

Error, error… does not compute! Syntax Errors – Typing Errors

Errors in spelling and grammar (syntax). “Doag. Bites, Man”

You can use the compiler or interpreter to uncover syntax errors.

You must have a good working knowledge of error messages to discover the cause of the error.

Semantic Errors – Logic or Meaning Errors Errors that indicate the logic used when coding the program

failed to solve the problem. “Man bites dog.”

You do not get error messages with logic errors. Your only clue to the existence of logic errors is the

production of wrong solutions. Run-time Errors (Exceptions)

Code does something illegal when it is run (hence runtime) E.g., divide by zero

Syntax refers to the structure of a program and the rules about that structure

In-Class Exercise

Write an algorithm that will, given the current date, find the date of the next day.

Pseudo-code Solution 1) Get the current date

      - Get the current month, day, and year in numerical form

2) If month is 2,        If day = 29 or day = 28 and it's not a leap year            increment month        else            increment day    else if month = 1,3,5,7,8,10,12        If day = 31            increment month        else            increment day    else if month = 4,6,9,11        If day = 30            increment month        else            increment day

3) Report "new" date [month, day, year]

Increment Day      add 1 to current day

Increment Month      if month = 12            increment year      else            add 1 to current month      day = 1

Increment Year      add 1 to current year      month = 1

Leap Year      divisible by 400 or divisible by 4 but not 100

In-Class Exercise

Write the pseudo-code for a Game of Monopoly

Write the pseudo-code for one person’s move as a procedure

Draw a flowchart representing one person’s move as a procedure

Pseudo-Code Solutions This is the pseudocode for a Game of Monopoly, including one person's move as a

procedure:

Main Procedure Monopoly_Game Hand out each player's initial money. Decide which player goes first. Repeat Call Procedure Monopoly_Move for next player. Decide if this player must drop out. Until all players except one have dropped out. Declare the surviving player to be the winner.

Procedure Monopoly_Move Begin one's move. Throw the dice. Move the number of spaces on the board shown on the dice. If the token landed on "Go to Jail," then go there immediately. Else if the token landed on "Chance" or "Community Chest," then draw a card and follow its instructions. Else follow the usual rules for the square (buying property, paying rent, collecting $200 for passing "Go", etc.). End one's move.

Flowchart Procedure Solution

One Person’s Move: