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C++ Plus Data Structures

Nell Dale

Chapter 1

Software Engineering Principles

Modified from the Slides made by Sylvia Sorkin, Community College of Baltimore County - Essex Campus

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Software Design Process

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Programming Life Cycle Activities

Problem analysis understand the problem

Requirements definition specify what program will do

High- and low-level design how it meets requirements

Implementation of design code it

Testing and verification detect errors, show correct

Delivery turn over to customer

Operation use the program

Maintenance change the program

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Software Engineering

A disciplined approach to the design, production, and maintenance of computer programs

that are developed on time and within cost estimates,

using tools that help to manage the size and complexity of the resulting software products.

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Toolboxes:

Hardware. Software Ideaware (focus of the course!): the

shared body of knowledge that programmers have collected over time, including algorithms, data structures, programming methodologies, tools…

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An Algorithm Is . . .

A logical sequence of discrete steps that describes a complete solution to a given problem computable in a finite amount of time.

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Goals of Quality Software

It works. It can be read and understood.

It can be modified.

It is completed on time and within budget.

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Specification: Understanding the Problem

Detailed Program Specification

Tells what the program must do, but not how it does it.

Is written documentation about the program.

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Writing Detailed Specifications

Detailed Program Specification Includes: Inputs

Outputs

Processing requirements

Assumptions

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Program Design

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Abstraction

A model of a complex system that includes only the details essential to the perspective of the viewer of the system.

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Information Hiding

Hiding the details of a function or data structure with the goal of controlling access to the details of a module or structure.

PURPOSE: To prevent high-level designs from depending on low-level design details that may be changed.

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Two Approaches to Building Manageable

Modules

Divides the problem into more easily handled subtasks, until the functional modules (subproblems) can be coded.

Identifies various objects composed of data and operations, that can be used together to solve the problem.

FUNCTIONALDECOMPOSITION

OBJECT-ORIENTED DESIGN

FOCUS ON: processes FOCUS ON: data objects

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FindWeighted Average

PrintWeighted Average

Functional Design Modules

Main

Print Data

Print Heading

Get DataPrepare File for Reading

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Object-Oriented DesignA technique for developing a program in which

the solution is expressed in terms of objects -- self- contained entities composed of data and operations on that data.

Private data

<<

setf...

Private data

>>

get...

ignore

cin cout

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More about OOD

Languages supporting OOD include: C++, Java, Smalltalk, Eiffel, and Object-Pascal, C, …

A class is a programmer-defined data type and objects are variables of that type.

In C++, cin is an object of a data type (class) named istream, and cout is an object of a class ostream. Header files iostream.h and fstream.h contain definitions of stream classes.

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Procedural vs. Object-Oriented Code

“Read the specification of the software you want to build. Underline the verbs if you are after procedural code, the nouns if you aim for an object-oriented program.”

Brady Gooch, “What is and Isn’t Object Oriented Design,” 1989.

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Verification of Software Correctness

• Testing• Debugging• Program verification

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Program Verification is the process of determining the degree to which a software product fulfills its specifications.

Program Verification

PROGRAM

SPECIFICATIONS

Inputs

Outputs

Processing Requirements

Assumptions

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Program Testing

Testing is the process of executing a program with various data sets designed to discover errors.

DATA SET 1

DATA SET 2

DATA SET 3

DATA SET 4

. . .

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Origin of Bugs

Various Types of Errors:

Design errors occur when specifications are wrong

Compile errors occur when syntax is wrong

Run-time errors result from incorrect assumptions, incomplete understanding of the programming language, or unanticipated user errors.

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Design for Correctness

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Robustness

Robustness is the ability of a program to recover following an error; the ability of a program to continue to operate within its environment.

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An Assertion Is a logical proposition that is either true or

false (not necessarily in C++ code).

EXAMPLES

studentCount is greater than 0

sum is assigned && count > 0

response has value ‘y’ or ‘n’

partNumber == 5467

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Preconditions and Postconditions

The precondition is an assertion describing what a function requires to be true before beginning execution.

The postcondition describes what must be true at the moment the function finishes execution.

The caller is responsible for ensuring the precondition, and the function code must ensure the postcondition. FOR EXAMPLE . . .

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Design Review Activities

Deskchecking: tracing an execution of a design or program on paper (checklist Fig1.4, pg31).

Walk-through: a verification method in which a team performs a manual simulation of the program or design.

Inspection: a verification method in which one member of a team reads the program or design line by line an the others point out errors.

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Program Testing

Unit Testing: testing a module or function by itself

Data Coverage: testing all possible input values (Black Box Testing)

Code Coverage: testing program paths (Clear/White Box Testing)

Test Plans Planning for Debugging Integration Testing

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Tasks within each test case:

determine inputs that demonstrate the goal.

determine the expected behavior for the input.

run the program and observe results.

compare expected behavior and actual behavior. If they differ, we begin debugging.

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Integration Testing

Is performed to integrate program modules that have already been independently unit tested.

FindWeighted Average

PrintWeighted Average

Main

Print Data

Print Heading

Get DataPrepare File for Reading

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Integration Testing Approaches

Ensures correct overall design logic.

Ensures individual moduleswork together correctly, beginning with the lowest level.

TOP-DOWN BOTTOM-UP

USES: placeholder USES: a test driver to callmodule “stubs” to test the functions being tested.the order of calls.

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Practical Considerations

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Life-Cycle Verification Activities:

Analysis Design Code Test Delivery Maintenance