Chapter2 ProblemSolving New

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Principles of Programming - NI July 2005 1

Chapter 2: Problem Solving

In this chapter you will learn about:Introduction to Problem Solving

Software development method (SDM)

Specification of needsProblem analysis

Design and algorithmic representation

Implementation

Testing and verificationDocumentation


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Software Development Method (SDM)

1. Specification of needs2. Problem analysis

3. Design and algorithmic representation

4. Implementation5. Testing and verification

6. Documentation


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Specification of Needs

To understand exactly:what the problem is

what is needed to solve it

what the solution should provideif there are constraints and special

conditions.


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Problem Analysis

In the analysis phase, we should identify thefollowing:

Inputs to the problem, their form and the input

media to be used

Outputs expected from the problem, their form

and the output media to be used

Special constraints or conditions (if any)

Formulas or equations to be used


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Design and algorithmic representation

Can be represented using pseudocodes orflowcharts



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Control Structure

In order to tackle a problem, we needa correct algorithm

to apply the algorithm at the 'good' moment

to decide which algorithm to apply (sometimes

there are more than one, depending onconditions)

to know if a certain operation must be repeated

In short: we need a suitable Control Structu re

In 1966, two researchers, C. Bohn and G. Jacopini,demonstrated that any algorithm can be described

using only 3 control structures: sequence,

select ionand repeti t ion.


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Pseudocodes

A pseudocode is a semiformal, English-like

language with limited vocabulary that can be

used to design and describe algorithms.

Criteria of a good pseudocode:

Easy to understand, precise and clear

Gives the correct solution in all cases

Eventually ends


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Pseudocodes: The Sequence control structure

A series of steps or statements that are executed inthe order they are written in an algorithm.

The beginning and end of a block of statements canbe optionally marked with the keywords begin andend.

Example 1:

Begin

Read the birth date from the user.

Calculate the difference between the

birth date and todays date.Print the user age.

End


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Pseudocodes: The Selection control structure

Defines two courses of action depending on theoutcome of a condition. A condition is an expressionthat is, when computed, evaluated to either true orfalse.

The keyword used are ifand else.

Format:

if condition

then-part

elseelse-part

end_if

Example 2:

if age is greater than 55

print Pencenelse

print Kerja lagi

end_if


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Pseudocodes: The Selection control structure

Sometimes in certain situation, we may omit the else-part.

if number is odd number

print This is an odd number

end_if

Nested selection structure: basic selection structure thatcontains other if/else structure in its then-part or else-part.

if number is equal to 1print One

else if number is equal to 2print Two

else if number is equal to 3print Three

elseprint Other

end_if

Example 3

Example 4


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Pseudocodes: The Repetition control structure

Specifies a block of one or more statementsthat are repeatedly executed until a conditionis satisfied.

The keyword used is while.

Format:

while condition

loop-body

end_while


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Example 5: Summing up 1 to 10

set cumulative sum to 0

set current number to 1

while current number is less or equal to 10

add the cumulative sum to current numberadd 1 to current number

end_while

print the value of cumulative sum


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Example 9:while user still wants to playbeginSelect either to play on network or play against computerif play on network

create connection to remote machineplay game with connected computerElseselect missionplay game locallyend_ifAsk user whether he/she still wants to playendend_while

For readability, always use properindentation!!!


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Flowcharts

Flowcharts is a graph used to depict or showa step by step solution using symbols whichrepresent a task.

The symbols used consist of geometrical

shapes that are connected by flow lines.

It is an alternative to pseudocoding; whereasa pseudocode description is verbal, aflowchart is graphical in nature.


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Flowchart Symbols cont

Selection symbol - shows a selection process

for two-way selection.

Off-page connector - provides continuation

of a logical path on another page.

On-page connector - provides continuation

of logical path at another point in the same

page.

Flow lines - indicate the logical sequence of

execution steps in the algorithm.


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Flowchart sequence control structure

Statement 2

Statement 1

Statement 3

:


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Flowchart selection control structure

Condition

else-

statement(s)

then-

statement(s)

YesNo


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Flowchart repetition control structure

ConditionLoop

Statement(s)

yes

no


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Flowchart example 1

Begin

Read birth date

Calculate

Age = current year birth date

Display

age

End


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Flowchart example 2

Begin

Read age

End

Age > 55? NOYES

print Pencen print Kerja lagi


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Flowchart example 5

Begin

End

current_number


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Implementation

The process ofimplement ingan algorithm bywriting a computer program using a programminglanguage (for example, using C language)

The output of the program must be the solution

of the intended problemThe program must not do anything that it is notsupposed to do

(Think of those manyviruses, buf fer o verf lows,

t ro jan h orses, etc. that we experience almost daily. Allthese result from programs do ing morethan they

were intended to do)


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Testing and Verification

Program testing is the process of executing aprogram to demonstrate its correctness

Program verification is the process ofensuring that a program meets user-

requirement

After the program is compi led, we must runthe program and test/verify it with differentinputs before the program can be released tothe public or other users (or to the instructorof this class)


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Documentation

Contains details produced at all stages of theprog ram development cyc le.

Can be done in 2 ways:Writing comments between your line of codes

Creating a separate text file to explain theprogram

Important not only for other people to use ormodify your program, but also for you to

understand your own program after a long time(believe me, you will forget the details of yourown program after some time ...)


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Documentation cont

Documentation is so important because:You may return to this program in future to use thewhole of or a part of it again

Other programmer or end user will need someinformation about your program for reference ormaintenance

You may someday have to modify the program, or maydiscover some errors or weaknesses in your program

Although documentation is listed as the last

stage of software development method, it isactually an ongoing process which should bedone from the very beginning of the softwaredevelopment process.


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Volume calculation

Write a pseudocode and a flowchart for a Cprogram that read the value of the height,width and length of a box from the user andprint its volume.


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Calculating Electricity Bills

The unit for electricity usage is kWh. Fordomestic usage, the monthly rate is 21.8cents/unit for the first 200 unit, 25.8cents/unit for the next 800 units and 27.8cents/unit for each additional units. Giventhe amount of electricity units (in kWh) usedby a customer, calculate the amount ofmoney needs to be paid by the customer toTNB. A bill statement needs to be printed

out.Write a pseudocode and a flow chart tosolve the above problem.


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Sum of 1 to n

Write a pseudocode and a flowchart for aprogram that reads a positive integernandthen computes and prints the sum of allintegers between 1 and n.


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Summary

This chapter introduced the concept ofproblem solving-a process of transforming thedescription of a problem into a solution.

A commonly used method SDM which

consists of 6 steps

3 basic control structures : sequence,selection and repetition structures

Pseudocode vs. Flow chartT.H.E E.N.D

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Chapter2 ProblemSolving New