Transcript C++ Plus Data Structures Nell Dale Software Engineering Principles Chapter 1

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
FUNCTIONAL
DECOMPOSITION
OBJECT-ORIENTED
DESIGN
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.
FOCUS ON: processes
FOCUS ON: data objects
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Functional Design Modules
Main
Prepare
File for
Reading
Get Data
Print Data
Find
Weighted
Average
Print
Weighted
Average
Print Heading
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Object-Oriented Design
A 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.
cin
cout
<<
>>
get
.
.
.
Private data
setf
.
.
.
Private data
ignore
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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

Program Verification is the process of
determining the degree to which a
software product fulfills its specifications.
SPECIFICATIONS
Inputs
Outputs
PROGRAM
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.
Main
Prepare
File for
Reading
Get Data
Print Data
Find
Weighted
Average
Print
Weighted
Average
Print Heading
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Integration Testing Approaches
TOP-DOWN
BOTTOM-UP
Ensures correct overall
design logic.
Ensures individual modules
work together correctly,
beginning with the
lowest level.
USES: placeholder
module “stubs” to test
the order of calls.
USES: a test driver to call
the functions being tested.
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Practical Considerations
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Life-Cycle Verification
Activities:
Analysis
 Design
 Code
 Test
 Delivery
 Maintenance

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