Lecture 3 Problem Solving

7/31/2019 Lecture 3 Problem Solving

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Alexandria University

Faculty of Science

Computer Science Department

Introduction to Programming(CS 102)


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The Program Development Life

Cycle

Creating new programs is called programdevelopment.

Creating successful applications requires planning Computer professionals need to develop new ormodified applications from time to time The process associated with creating successful

applications programs is called the programdevelopment life cycle (PDLC).


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The Program Development Life Cycle


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1. Problem Analysis

During analysis, a systems analyst andprogrammer: review specifications, and

talk with users to fully understand what the softwareshould do.

Documentation consists of: program specifications,

timetable,

which language will be used,

how the program will be tested, and

what documentation is required.


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2. Program Design

Program design: stage where program

specifications are expanded into a complete

design of the new program.

Structured programming and object-oriented

programming are two of the most significant

approaches to the design process.


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Program Design:

Program Design Tools

Program design tools are planning tools.

Structure charts

Program flowcharts

Pseudocode

Data modeling


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Structure Charts

Structure charts depict the: overall organization of a program, and how the modules of a program are defined and how they connect to each other hierarchically.

Program modules should be arranged hierarchically in atop-downfashion Why?? So that their relationship to each other is apparent.


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Flowcharts Use geometric symbols and familiar relational operatorsto provide a graphic display of the sequence of stepsinvolved in a program

Different symbols are used to represent different actionssuch as

Start/stopDecisionInput/outputProcessingLooping symbols


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Pseudocode

Uses English-like statements in place of the graphic symbolsof the flowchart.

Unlike a flowchart, pseudocode is easy to modify and canbe embedded into a program as comments.

No standard set of rules exists for writing pseudocode,although a number of conventions have been developed.


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Program Design:

Program Design Tools

Data modeling

is a technique used to illustrate the data in an applicationand is frequently used with object-oriented programming.

In a data model, the objects in the program are identified,along with their variables and class.


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3. Program Coding

Coding: actual process of creating theprogram in a programming language.

Programming language must be chosen.

Coding standards should be adhered to. Make use of reusable code and data dictionaries.

Translate coded programs into executable code.

Documentation results in finished sourcecode.


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3. Program Coding contd

The coded program is referred to as source code. To beexecuted, the program is converted by the computerto object code using a special program.

Acompiler translates the entire program into machine

language before executing it. The program then doesntneed to be recompiled until it is modified.

An interpreter translates program statements one at atime. Interpreters are helpful during the debugging

stage, but are slower during execution of the finishedprogram.

An assembler converts assembly-language statementsinto machine language.


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4. Program Debugging and Testing

Debugging: process of making sure a program

is free of errors or bugs.

Preliminary bugging often finds syntax or logic

errors.

Testing can consist of alpha or beta testing.

Documentation includes a copy of the finishedprogram code, plus test data and results.


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4. Program Debugging and Testing

contd

Preliminary debugging begins after the program has beenentered into the computer system.

Rarely is a program error-free the first time it runs.

Two common types of errors are syntax errors and logicerrors: Asyntax error occurs when the programmer has not followed the

rules of the language.

Alogic error, or execution-time error, results when the commandsyntax is correct but the program is producing incorrect results.


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5. Program Maintenance

Programmaintenance: process of updating

software so that it continues to be useful.

A costly process, but can be used to extend the

life of a program.

Documentation consists of amended program

package reflecting what problems occurred

and what program changes were made.


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What Is a Programming Language?

Aprogramming language is a set of rules used to writeinstructions to the computer.


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Categories of Programming Languages

Low-level languages

High-level languages

Fourth-generation languages (4GLs)

Natural and visual languages


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Machine and Assembly Languages Machine and assembly languages are called low-level

languages

Programmers who code in them must write instructions atthe finest level of detail, the base level of the hardware

Virtually no one writes machine-language programsanymore

All programs must be translated by a language translatorinto machine language before they are executed

Assembly languages are fast and consume little storagewhen compared with higher-level languages, but takelonger to write and maintain


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High-Level Languages

High-level languages differ from their low-levelpredecessors in that they require less coding detail andmake programs easier to write.

Programs written in a high-level language (BASIC,COBOL, Pascal, C, etc.) need to be translated into

machine language before they can be executed.


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Fourth Generation Languages (4GL) Very-high-level languages that are much easier to use

than the high-level languages They are declarative rather than procedural languages. For instance, to draw a bar chart in a procedural

language, you must tell the computer how to draw barsand where to place them.

In a declarativelanguage, you may be able to just point

to the data you want graphed, click several menuchoices, and youre in business.

Fourth-generation languages are commonly used toaccess databases (query languages).


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Popular Programming Languages

FORTRAN

COBOL

Pascal

n BASIC and Visual Basic

n C, C++, AND C#

n Java


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Markup Languages

Markup languages use symbols or tags todescribe what a document should look likewhen displayed.

HTML (Hypertext Markup Language)

Dynamic HTML

XML(extensible markup language)

XHTML (extensible Hypertext Markup Language)

WML (Wireless Markup Language )


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Scripting Languages

Scripting languages are used to build programinstructions into Web pages, usually to adddynamic content.

JavaScript

VBScript

Perl


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FLOWCHARTS

Understanding the basic parts of the flowchartand the advantages and limitations of

flowcharts.


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Definition

Flowcharts a diagrammatic representation

that illustrates the sequence of operations to

be performed to get the solution of a

problem.


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How to Write a Program?

1. Start2. Define Problem to Solve

3. Think of an Algorithm

4. Think of a Technique for the Solution

5. Write Solution on a Piece of Paper

6. If not Finished Repeat Steps 4 and 5

7. Write Code and Program

8. Debug and Test9. If not Finished Repeat Steps 7 and 8

10. Stop


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How to Write a Program?

Define Problem to Solve

Stop

Think of an Algorithm(Technique for the solution)

Idea!!!!

Write it downon a piece of paper(before you forget it!!!)

Write Code andProgram

JobDone

Debug and Test

JobDone

Start

Think of aTechnique for the solution

No

Yes

YesNo


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Algorithms

A computer program makes use of algorithms

Algorithm is a complete step-by-step

procedure for solving a problem or

accomplishing a task.


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A1

Off-pageConnector

? Yes

No

Condition

CalculateVariables

Process Rectangle

A

On-Page

Connector

PrintResults

Input/OutputStart Or StopProcess

Start

Standard Flowchart Symbols


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Example of Flow Charts


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Basic Flow Chart Operations

All computer instructions are based on four

basic processing patterns:

Simple Sequence

Selection Pattern

Loop Pattern

Branch Pattern


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Simple Sequence

Logic involves executing instructions one

statement after another, in the order

presented by the program.

This is the simplest and most-used pattern.

The computer assumes that all instructions

are to be executed in this order unless the

program presents other instructions.


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Read Names

Compare with Criteria

Print Eligible Names

Example of a Simple Sequence


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Selection Pattern

Requires that the computer make a choice

among two or more items.

Each choice is based on one of two

comparisons a computer can make: true or

false (Yes or No).


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?HonourStudent

List underStudent Loan

Yes

List underScholarships

No

Example of a Selection Pattern


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Loop Pattern

Causes an interruption in the normal sequence of

processing and directs the computer to loop back

to a previous statement in the program,

repeating the same sequence over again, usuallywith new data.

By looping, the programmer avoids having to

repeat the same set of instructions over and over.


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?

MoreNames

No

Yes


Print Eligible Names

Example of a Loop Pattern


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Branch Pattern

Is often used in combination with selection orlooping.

The branch pattern allows the computer to skip

statements in a program. The branch encourages undisciplined jumping

around among program statements, acharacteristic that is frowned on by most

programming experts. Branching is difficult to follow and is an inefficient

use of computer power.


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?

HonourStudent

No

Yes

Read Area of Concentration

Read Courses Taken


1

1

Example of a Branch Pattern


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Types of Flowcharts

1. Functional Chart A chart that is used to describe how activities interact with one another

within an organization as well as with other organization and/or systems.

2. Process Flow Chart

A chart that is used to describe the sequence and relationship of the tasks

that make up an activity

3. Process Flow Description Chart Detailed description of the tasks outlined in a Process Flow Chart

Typically used to show the kinds of tasks performed within a process (thenumber of operations, review, and transfers; and the amount of storage andtime required to complete an activity)


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Uses of Flowcharts Flowcharts are generally drawn in the early stages of formulating

computer solutions.

Flowcharts facilitate communication between programmers andbusiness people.

Flowcharts play a vital role in the programming of a problem and

are quite helpful in understanding the logic of complicated andlengthy problems.

Once the flowchart is drawn, it becomes easy to write theprogram in any high level language.

Often we see how flowcharts are helpful in explaining the

program to others. Hence, it is correct to say that a flowchart is a must for the better

documentation of a complex program.


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Advantages of Flowcharts

Communication: Flowcharts are better way ofcommunicating the logic of a system to allconcerned.

Effective Analysis: With the help of flowchart,problem can be analysed in more effectiveway.

Proper Documentation: Program flowcharts

serve as a good program documentation,which is needed for various purposes.


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Disadvantages of Flowcharts

Complex Logic: Sometimes, the program logic isquite complicated. In that case, flowchartbecomes complex and clumsy.

Alterations and Modifications: If alterations are

required the flowchart may require re-drawingcompletely.

Reproduction: As the flowchart symbols cannotbe typed, reproduction of flowchart becomes a

problem. The Essentials of what Is Done can easily be lost

in the technical details of how it is done


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Case Study - 1

A certain Company gives each of its sales

people $1,000 at the beginning of each month

to cover travel, lodging, and food expenses.

At the end of the month, a salesperson must

total his/her expense receipts. If the amount is

less than $1,000 then the difference must bereturned to the company.


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Case Study 1 (Solution)

Here is an algorithm for figuring how much

money, if any, must be returned:

1. Total the expense receipts for the month.

2. Subtract the amount of the expense receipts

from 1,000.

3. If the remainder is more than 0, return that

amount to the company.


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Stop

Subtract ExpensesR


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Case Study 1 (Solution 1)

Assume the Employee has Spent $1250

What would be the amount to return to the

company in this case?


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Stop

Subtract ExpensesR


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Now Assume the Employee has spent $950

What would be the amount to return to the

company in this case?


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Stop

Subtract ExpensesR = 1000-E

?E


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Basic Guidelines for Flowcharts

Only one flow line

should come out

from a process

symbol.


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Only one flow line

should enter a

decision symbol, but

two or three flowlines, one for each

possible answer,

should leave thedecision

symbol.

Y

N

?


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Only one flow line is

used in conjunction

with terminal

symbol.

Stop

Start


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Ensure that the flowchart has a logical start

and finish.

It is useful to test the validity of the flowchart

by passing through it with a simple test data.


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Case Study - 2

Draw a flowchart to find the sum of first 5

natural numbers.

Start


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10

Case Study - 2Sum = 0

Stop

N = 0

N = N + 1

?N = 5

Start

Sum = Sum + N

No

Yes

N Sum

0 0

1 1

2 3

3 6

4

5 15Print Sum


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Case Study - 3

Draw a flowchart to find the largest of three

numbers A,B, and C.


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Case Study - 3

Stop

?A > B

Start

No

Read A, B, C

?B > C

No

?A > C

No

Print B Print C Print APrint C

Yes Yes Yes


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Case Study 3 - (Solutions)

Consider four input cases:

1. A = 5 ; B = 7 ; C = 3

2. A = 5 ; B = 3 ; C = 73. A = 5 ; B = 3 ; C = 3


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Stop

?A > B

Start

No

Read A, B, C

?B > C

No

?A > C

No


Yes Yes Yes

B = 7

C = 3

A = 5


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Stop

?A > B

Start

No

Read A, B, C

?B > C

No

?A > C

No


Yes Yes Yes

B = 3

C = 7

A = 5


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Stop

?A > B

Start

No

Read A, B, C

?B > C

No

?A > C

No


Yes Yes Yes

B = 3

C = 3

A = 5

Documents

Lecture 3 Problem Solving