Problem Solving & Flow Charts

8/2/2019 Problem Solving & Flow Charts

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Working With Algorithm andFlowcharts

Understanding theirpracticality


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What is an Algorithm?

It is a finite set of rules giving a sequence of

operations for solving a specific type ofproblem.

In most common computer applications an

algorithmic solution to a problem must beconstructed.


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Design of an Algorithm

The design of an algorithm tends to be difficult

when the task is non-trivial. Computers tend to lack the intuition or

common sense to realise the full procedure.

The designer must describe the procedure very

precisely for it to function properly

Top-down design approach is often used.


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How does the top-down method

work?

First try to break the process into a number of

steps, which are smaller and simpler than thatfor the entire process.

The sub-algorithms can themselves be brokendown into smaller portions

We use flow charts to show how the algorithmwill work.


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Lets take a look at an algorithm

Image you had to program a robotto make coffee.


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A Simple Algorithm : Making Coffee

Algorithm

1 Boil water

2 Put coffee


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Original First Refinement

1 Boil water

2 Put coffee

1.1 fill kettle1.2 switch kettle on

1.3 wait until boiling

1.4 switch off kettle

2.1 open coffee jar

2.2 Fill spoon withcoffee

2.3 tip spoonful intocup

2.4 close coffee jar


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Original First Refinement Second Refinement

1 Boil water

2 Put coffee

1.1 fill kettle1.2 switch kettle on

1.3 wait until boiling

1.4 switch off kettle

2.1 open coffee jar

2.2 Fill spoon withcoffee

2.3 tip spoonful intocup

2.4 close coffee jar

1.1.1 put kettle undertap

1.1.2 turn on tap

1.1.3 wait till kettle is full

1.1.4 turn off tap

2.1.1 take coffee jarfrom shelf

2.1.2 remove lid

2.4.1 put lid on coffeejar

2.4.2 replace coffee jaron shelf


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Selection (Decision Statement)

An algorithm which is solely a sequence of

steps is extremely inflexible A What if ? Then Statement allows for this

flexibility.

What if the coffee jar is empty?

Then get a new jar.


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Iteration (Repetition or Loop)

Sometimes it is necessary for the computer not

just to make a decision, but a continuousaction.

This processes is called iteration.

Example : With the robot making the coffee

Continue filling coffee jar untiljar isfound.


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What Is a Flowchart?

A diagrammatic representation of a program

Building a flowchart is like putting a puzzletogether; there are standard pieces

The standard action shapes include terminal,process, in/output, decision and junction.


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What Are the Basic Symbols?

A program should

always begin with a startsymbol and finishsymbol

For Pascal it equals thebegin and the end

Start

End


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Whenever a decisionmust be taken a

diamond symbol is used.

Can you see thecorrelation to the

ifthenelsestatements.

no

Is mark

> 50?

yes

Decision/ Comparison

Operation


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Used to connect differentparts of the programtogether.

Connector


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A rectangle represents aprocess.

When a variable mustbe assigned to a value, aprocess must be used

When clearing the

screen, changing coloura rectangle must beused

mark := 0

Process to be

performed


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Input and Output arerepresented using a

parallelogram.

In Pascal we are dealingwith writeln, write, or

readln.Show resultto user

Read markfrom user

Input /Output

Operation


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Lets Put the Pieces Together!

Example

You are going to school, how will

you get there?


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Leave the House


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Leave the House

Check the Weather


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Leave the House

Check the Weather

Weather

Clear?


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk

Arrive at School


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk

Arrive at School

No, Rain.


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk

Arrive at School

No, Rain.Put on raincoat


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk

Arrive at School


Ride Bus


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Leave the House

Check the Weather

Weather

Clear?

Yes

Walk

Arrive at School


Ride Bus

Problem Solving & Flow Charts

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