CS2006 - Data Structures I

Chapter 2Principles of Programming

& Software Engineering

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Topics

Software Life Cycle

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Introduction

How do you write a Java program? Old fashion way

Write code Compile Check syntax Run Check logic

How long will this take? Which phase takes more time?

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Introduction

A better way Systematic way (Structured approach)

Specify problem Analyze Design Implement Test Maintain

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Introduction

SW Engineering: Computer science branch that provides

techniques for development of computer programs

Systematic approach to analyze, design, implement, and maintain software

Uses CASE tools

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The Software Life Cycle

1. Specification

2. Design

3. Risk Analysis

4. Verification

5. Coding

6. Testing

7. Refining

8. Production

9. Maintainence

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1. Specification & Analysis

Specification A contract between the module and any other

module using it Doesn't include information about how the

task is to be performed or the method of solution, but what

May involve construction of a prototype program to get more details from users.

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1. Specification & Analysis

Example: “begin & write a software to store a library’s

catalogue of books” Input:

Librians enter new books as they arrive Library users enter search keys to search

through our list

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1. Specification & Analysis

Process: Add new book Search for books

Output: Show all the info about a book

Requirements What type of processing is required Are there any time/space/performance constraints

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2. Design

Given: Clear & detailed specification of all aspects of

the problem Output:

Design for a solution to the problem Idea:

Use modular design Divide & conquer Divide the problem into smaller manageable parts.

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2. Design

Generate an outline of the problem solution. Requires breaking the entire problem down into

small manageable parts - modules. Modules are self-contained units of code.

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2. Design

Design Example: Sort Function Purpose:

Sort an array of integers

Specification: Receive an array of N integers (input), where N > 0

(assumption) Return the array (output) with the integers sorted (action)

Remember: Specification is a contract

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2. Design

Design Example: Sort Function First-draft specification:

Sort(A, N)

// Sorts an array

// Precondition: A is an array of N integers; N > 0

// Postcondition:Integers in A are sorted

What is missing?

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2. Design

Design Example: Sort Function Revised Specification:

Sort(A, N)// Sorts an array of MAX_ARRAY elements// Precondition:// A is an array of N integers;// and 1 <= N <= MAX_ARRAY, // where MAX_ARRAY is a global constant// that specifies the maximum size of A// Postcondition:// A [0] <= A [1] <= . . . <= A [N-1],// N is unchanged

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3. Risk Analysis

Risks are primarily business related but can be personal as well.

Example: If a piece of software is not ready in time the company may lose the market to a competitor.

Not an important issue for this course.

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4. Verification

Determining the degree to which a software product fulfills its specification

Formal, theoretical methods for proving algorithm correctness

Assertion (Predicate): Statement about a particular condition at certain point

in an algorithm Invariant:

Condition that is always true at a certain point in an algorithm

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5. Implementation (Coding)

Coding Translating the algorithm into a particular

programming language & removing syntax errors

Should not start unless previous stages are well defined

Original solution usually simplified

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5. Coding

Bottom-up implementation: First implement submodules, then modules

Top-down implementation: Implement a module before implementing its

submodules Use stubs Refinement might be needed Stubs:

Dummy functions that do nothing and are placed in the place of submodules to focus attention on the module itself

A

S3S2S1

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6. Testing

Careful design of test data is important Valid (In-range) data Invalid (out-of-range) data Random values of data

Test several times on different circumstances

Any modification in the program needs re-testing

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7. Refining the Solution

Usually involves increasing the "robustness" of a solution.

Often simplifying assumptions are made in the design process that must be removed from final versions.

Example: assume that the input will be be integers between 0 and 1000.

During this step code would be inserted to actually test the input values.

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8. Production

Distribute the SW product to its intended users

Install the SW Use the SW

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9. Maintenance

Correct errors not discovered during testing

Add more features Enhance existing features Modify to suit the user better

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Review The first phase of the life cycle of software

is the ______ phase. design risk analysis specification coding

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Review The syntax errors of a program are

removed during the ______ phase of the program’s life cycle. verification coding testing refining maintenance

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Review Which of the following is an example of a

logical error? an algorithm that calculates the monthly payment

of a loan displays incorrect results an array subscript in a program goes out of range a program expects a nonnegative number but

reads –23 the beginning of a while loop is written as “whille”

instead of “while”

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Review During the design phase of the software

life cycle, the program is divided into ______. invariants loops Modules prototypes

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Review A prototype program is created during the

______ phase of the software life cycle. design specification Coding testing