1 technology in action chapter 7 behind the scenes: software programming

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Technology in Action

Chapter 7

Behind the Scenes: Software Programming

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Chapter Topics Life cycle of a program Problem statement Algorithms Moving from algorithm to code Moving from code to machine language Testing programs Completing a program Selecting the right programming language Most popular programming languages

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Computer Programming and Software Engineering

The instructions that make up a computer program are sometimes referred to as code

Programs can have millions of lines of code Developed by computer programmers

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Programming Languages

Programming languages are made up of keywords and grammar rules designed for creating computer instructions

Low-level languages typically include commands specific to a particular CPU or microprocessor family

High-level languages use command words and grammar based on human languages

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The Life Cycle of a Program Programming is the process of translating a

task into a series of commands a computer will use to perform that task

Programming involves: Identifying the parts of a task the computer can

perform Describing tasks in a specific and complete

manner Translating the tasks into a language that is

understood by the computer’s CPU

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Program Development Life Cycle

Step 5Finishing the Project

Step 4Debugging

Step 3Coding

Step 2Making a Plan

Step 1Describing the Problem

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Step 1 : Describing the Problem

The problem statement is: The starting point of programming A description of tasks the program is to accomplish How the program will execute the tasks Created through interaction between the programmer and

the user

The program statement includes error handling and a testing plan

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PROGRAM GOAL: To compute the total pay for a fixed number of hours worked at a parking garage.

INPUTS: Number of Hours Worked........................ a positive number

OUTPUTS: Total Pay Earned ................................... a positive number

PROCESS: The Total Pay Earned is computed as $7.32 per hour for the first eight hours worked each day. Any hours worked beyond the first eight are billed at $11.73 per hour.

ERROR HANDLING:

The input Number of Hours Worked must be a positive real number. If it is a negative number or other nonacceptable character, the program will force the user to reenter the information.

TESTING PLAN: INPUT OUTPUT NOTES

8 8*7.32 Testing positive input

3 3*7.32 Testing positive input

12 8*7.32 + 4*11.73 Testing overtime input

–6 Error message/ask user to reenter value

Handling error

Parking Garage Example

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Step 2: Developing an Algorithm

Algorithm development: A set of specific, sequential steps

that describe what the computer program must do

Complex algorithms include decision points: Binary (yes/no) Loop (repeating actions)

Visual tools used to track algorithm and decision points:

Head off to cafe

Buy textbook

Go to accounting

lecture

Yes No

No

No

Yes

Yes

Wake Up

Check wallet for $

Do I have > $80

Go get gas

Did I get $80 from the ATM?

Do I have my credit card?

Go to the ATM for cash

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Flowchart and Pseudocode

Underlined words are information items that appear repeatedly in the algorithm.

1. Ask the user how many hours they worked today2. If the number of hours worked < = 8, compute total pay without overtime otherwise, compute total pay with overtime pay3. Print total pay

Bold terms show actions that are common in programming, such as reading data, making decisions, printing, and so on.

Flowchart Pseudocode

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Top-Down Design Problem is divided into a series of high-level tasks Detailed subtasks are created from high-level tasks

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Object-Oriented Analysis Object-oriented analysis Classes (categories of

inputs) are identified Classes are defined by

information (data) and actions (methods or behaviors)

Objects are defined by their class, data, and behavior

Interaction between classes is determined

Existing classes can be used for other projects

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Step 3: Coding Coding is translating an algorithm into a

programming language Generations of programming languages

increasing in demands on machines DEcreasing in demands on humans

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Programming Languages

First-generation languages Machine language (1's and 0's) Bits describe the commands (1011 0101)

Second-generation languages Assembly languages Words describe the commands ADD X, Y or MOV Y, 13 need a translator - an assembler program

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Programming Languages Third-generation languages

FORTRAN, BASIC, C, JAVA use symbols to describe commands TotalPay = Hours * Rate; More abstract, more like the way humans think

Fourth-generation languages SQL More power built into the language, human has to make

only a few choices - wizards, scripts uses sentences to describe commands Select all where State = KY and Rate > 5

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Programming Languages

Fifth-generation languages Hypothetical based on natural (human) languages

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Compilation

Compilation is the process of converting code into machine language

Compiler reads the source code and translates it into machine language

After compilation, programmers have an executable program

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Step 4: Debugging Running a program to find and fix errors is

known as debugging Debugger: Tool that helps programmers

locate logical errors Syntax vs. Semantics

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Syntax and Semantics

Syntax – the rules of a language - how statements are formed - punctuation, spelling, etc.

Semantics – the meaning of something said in that language - what does the computer do when that statement is executed?

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Step 5: Finishing the Project Users test the program (internal testing) Beta version released:

Information collected about errors before final revision

Software updates (service packs): Problems found after commercial release

Documentation created: User manuals User training

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Program Planning

Problem statement:

Givens:

two pizzas to compare

both pizzas contain the same toppings

the pizzas could be round or square

the prices, shapes, and sizes of the two pizzas

Result:

a message indicating which pizza has the lower price per square inch

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Program Coding

A program editor is a type of text editor specially designed for entering code for computer programs

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Program Coding

A IDE (integrated development environment) provides programmers with tools to build substantial sections of a program Form design grid Editor Compiler Linker Execution Debugger

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Program Testing

A computer program must be tested to ensure that it works correctly

Program errors include Syntax errors Logic errors (semantics) Runtime errors

A debugger can help a programmer read through lines of code and solve problems

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Program Documentation

Remarks or “comments” are a form of documentation that programmers insert into the program code

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Algorithms

Set of steps for carrying out a task that can be written down and implemented

Start by recording the steps you take to solve the problem manually

Specify how to manipulate information Specify what the algorithm should display as

a solution

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Expressing an Algorithm

Pseudocode If Shape1 is round then

squareinches1 is pi * (size1 / 2) squared otherwise

squareinches1 is size1 * size1 set SqInchPrice1 to Price1 / Squareinches1 while there are more pizzas

get their datacalculate SquareInchPrices

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Expressing an Algorithm

Flowchart

The pizza program flowchartillustrates how the computershould proceed through theinstructions in the final program.

CLICK TO START

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Expressing an Algorithm

Perform a walkthrough to make sure your algorithm works

"Tracing" a program - pretend to be the computer and see what the program does

Desk checking - trace the program with paper and pencil before putting it into the computer

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Structures

A programmer has to choose them Data structures

variables, strings, vectors and matrices, trees allow the programmer to manipulate the data with actions like addition, comparison, display

Control structures dictate the order the statements are executed in

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Control Structures

Sequence control structuresimplest structurestatements done in order from start to finishone entrance, one exitno unconditional transfers out of sequence

= "spaghetti code"

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Control Structures

Selection control structure

The computer executes a decisionindicated on the flowchart by the question in the diamond shape.

CLICK TO START

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Control Structures

Repetition control structure

To execute a loop, the computerrepeats one or more commands until some condition indicates that the looping should stop.

CLICK TO START

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Control Structures

Subroutines, procedures, and functions are sections of code that are part of the program, but not included in the main execution path

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Guarantees for Control Structures

One-entry-point, one-exit-point rule No infinite loops or logic errors No “Spaghetti Code” No dead code

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Programming Languages Selecting the right language:

Speed of execution, speed of development Organizational resources available

Space, programmers Type of target application Portability

Visual Basic

C / C++Java HTML

JavaScriptVBScript

ASP / JSP

Flash / XML

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FORTRAN - formula translator

The oldest high-level programming language; designed for scientific and mathematical applications.

John Backus

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COBOL - common business oriented language

designed for business transaction processing.

Grace

Hopper

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Pascal - named after Blaise Pascal, French scientist

designed to teach structured programming; useful for math and science applications.

Niklaus

Wirth

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Visual Basic Used to build Windows

applications Object-oriented

language Visual Basic 2005 is the

current version

Sample Visual Basic

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C and C++ C

Developed for system programmers

Combines high and low level programming features

Modern operating systems written in C

C++ Uses the same features

as C Includes object-oriented

design

Sample C

Sample C++

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Java Object-oriented features Large set of existing classes Architecture neutral Java applets: Small Java-based programs

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Web Applications

HTML/XHTML Hypertext Markup Language/Extensible Hypertext

Markup Language Not a true programming language Uses special symbols (tags) to control how Web

pages are viewed Extensible Markup Language (XML)

Enables computers to efficiently transfer information between Web sites

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Web Applications JavaScript

Used to make Web pages more visually appealing and interactive

VBScript A subset of Visual Basic Used to add interactivity to Web pages

PHP Another scripting language gaining popularity

Dynamic Decision Making Web page has the ability to display content based on user

choices

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Web Applications

Active Server Pages (ASP) and Java Server Pages (JSP) Adds interactivity capabilities to Web pages Translates user information into a request for

more information from a company’s computer Flash

Enables elaborate animations to be created for Web pages