MELJUN CORTES--T102_FLOWCHARTING_MELJUN_LECTURE

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Introduction To Flowcharting | SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2005 | Last Updated: July 2005 Slide 1

Introduction To

Flowcharting

MELJUN CORTES


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Todays Topics Flowchart Symbols

Control Structures

Some examples


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Flowchart:

Represents an algorithm in graphical symbols

Example: Algorithm for multiplying two

numbersS t a r t

S t o p

G e t A

G e t B

D i s p l a y t h e

R e s u lt C

C a l c u l a te R e s u t

C = A * B


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Terminal: Used to indicates the start and end of aflowchart. Single flow line. Only one Start and Stop

terminal for each program. The end terminal for

function/subroutine must use Return instead of Stop.

Process: Used whenever data is being manipulated. Oneflow line enters and one flow line exits.

Input/Output: Used whenever data is entered (input) ordisplayed (output). One flow line enters and one flow line

exits.

Decision: Used to represent operations in which there aretwo possible selections. One flow line enters and two flow

lines (labeled as Yes and No) exit.

Function / Subroutine: Used to identify an operation in a

separate flowchart segment (module). One flow line enters

and one flow line exits.

On-page Connector: Used to connect remote flowchartportion on the same page. One flow line enters and one

flow line exits.

Off-page Connector: Used to connect remote flowchartportion on different pages. One flow line enters and one

flow line exits.

Comment: Used to add descriptions or clarification.

Flow line: Used to indicate the direction of flow ofcontrol.

Flowchart Symbols


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Example:

S t r t

S t

d

d

is l t

s l t

lc l t s t*

Start Terminal.Program starts

here

Stop TerminalProgram endshere

Input.Enter values forA and B

Process

Output


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Comments or description

St

rt

d N,

M

N

Ys

St

N T n mb r f st d nts

M

T

nmb

r

f s

bj

cts


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Connectors on the same page

Start

2

1

1 2

Stop

1- connection on the same flowchart portion

2- connection on the different flowchart portion


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Connectors on a different page

Page 1 Page 2

St

rt

N

Y

s

St


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Function

Page 1

AVRG (result, 1, 2, 3)

Start

Stop

Rea

1, 2 , 3

Pri t

result

Page 2

AVRG ( result, 1, 2, 3)

Retur

su = 1+ 2+ 3

result = su /3

End terminal

must be a Return

Start terminal for aFunction is different.

Do not use Start

The detail of how the function worksis put in another flowchart.

This is known as Function-Definition

At this point,we only focus on whatto do. How to do it,it comes later.

This part is known asFunction-Call

Body of a function isthe same withnormal flowchart

This flowchart calculates the average of three numbers


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Related terms and concepts

Page 1


Start

Stop

Rea

1, 2 , 3

Pri t

result

Page 2

AVRG is the function name

Objects enclosed by ( ) result,n1, n2, n3 - are called parameters

Parameters used in a function-call

are called actual parameters

result, n1, n2, n3 are actual parameters

Parameters used in a function-definitionare called formal parameters

R, a, b, c are formal parameters

Each formal parameter representsan actual parameter accordingto its order:

R represents result,a represents n1,b represents n2,

c represents n3

The name of an actual parameter may bedifferent from its formal parameter



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Related terms and concepts (cont.)

Page 1 Page 2

In a function-definition, you should onlyuse formal parameters R, a, b, c

You shouldnt use actual parameters

This is wrong!n1, n2, n3 are actual parameters.Should use a, b, c instead.

This is wrong!R is an formal parameters.

Should use result instead.


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Page 1


Page 2

A function may becalled more than once

At this time:Rrepresents average1,a represents n1,b represents n2,c represents n3

When comes to this:

Rrepresents average2,a represents n4,b represents n5,c represents n6



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A function parameter may act as:

InputData of the function

Output

The result of the function

Both


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Page 1


Start

Stop

Rea

1, 2 , 3

Pri t

result

Page 2

Function call:

result is the output

parameter.n1, n2, n3 are the inputparameters.

Function definition:

R is the output parametera, b, c are input parameters




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Page 1 Page 2

Function call:

p and qact as both input and outputparameters.

Function definition:

x and y act as both input and outputparameters

This flowchart exchanges or swaps the valueof x and y each other


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Page 2


If there is only one output parameter, the flowchart may RETURN the result

Example: let take a look again at the function that calculates the average of three numbers.

Original function flowchart:

Page 2

Since it has only one output, the output is RETURN

The output parameter (R)is removed from the formalparameter list

and the result

is return


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Since the function flowchart has been modified, the way of the function to be called will also be changed

Original main flowchart: Modified main flowchart:

Page 1

AVRG (result,1,

2,

3)

Start

Stop

Rea

1, 2 , 3

Pri

t

result

Page 1

Now, result is not

anymore a parameterof the function-call


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Control Structure

Describe the flow of execution.

In flowcharts, flow of execution is represented bythe arrow line.

Types of control structure:Sequential

SelectionRepetition


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Sequential Structure

statement

statement

statement

Multiple statements considered as one statement

|

A statement means

a command or an instruction


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Selection Structure

If

(one-choice)

condition

statement

TRUE

FALSE |statement

If set condition is true, execute the statement, else do

nothing

do it or dont

condition


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Selection Structure (cont..)

If-else(two-choices)

condition

Statement 2Statement 1

|statement

If set condition is true, execute the first statement, elseexecute second statement

TRUE FALSE

do this one orthe other one

condition


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Considered asone statement

Nested if(if within if)


test1

test2

statement

FALSE

FALSE

TRUE

TRUE

|

test1

FALSE

TRUE

it is an one-choice if


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Complex if-else & if Statements

x

condition

statement

condition

statement

statement TRUE

TRUE

FALSE

FALSE

Considered as one statement



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Repetition Structure

while Loop

It is a pre-test loop

statement

condition

body of loop|

While a set condition is true, repeat statement (body of loop)

TRUE

FALSE

condition


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Repetition Structure (cont)

do-while Loop

It is a post-test loop

| statement

FALSE

TRUE

Do the statement (body of loop) while a condition is true

statement

condition


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for Loop

It is a pre-test loop

x

initialization

condition

bodyofloop

increment

y

FALSE

TRUE

Repetition Control Structure (cont)


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Example:

Start

Stop

Rea

Le gth,

Wi th

Pri t

Area,

Peri eter

Calculate Area

Area=Le gth * Wi th

Calculate Peri eter

Peri eter=

2 * (Wi th+Le gth)

Input:Length


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St rt

St

d N m

rint

" t r "

Y s

N m>0? N

rint

" t r "

Example:What is the output of the following flowchart when the input Num= 10

Num = 10

10 > 0 ? => YES

Input:Num > 10

Output:

Category A

Category A


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St rt

St

d N m

rint

" t r "

Y s

N m>0? N

rint

" t r "

Example:What is the output of the following flowchart when the input is Num= 0

Num = 0

0 > 0 ? => NOOutput:Category B

Input:Num >0

Category B

Output:

Category A

Category A


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Start

Stop

Pri t

Result

Result=Result + Cou t

Cout=Cou

t - 1

Iitialize

Result=

Cout=

u

Cout

!

Rea"

u

o

Pri

t Cou

t

Yes

Example:What is the output of the following flowchart when the input is Num= 4

Input:Num 4

Variables (in memory):

Num [ ]

Result [ ]

Count [ ]


Num [4 ]

Result [ ]

Count [ ]

Count = 4

4 > 0 ? => YES


Num [4 ]

Result [ 0 ]

Count [ 4 ]

Count: 4


Num [4 ]

Result [ 4 ] 0 + 4

Count [ 3 ] 4 - 1

Count: 3

Count = 3

3 > 0 ? => YES


Num [4 ]

Result [ 7 ] 4 + 3

Count [ 2 ] 3 - 1

Count: 2

Count = 2

2 > 0 ? => YES


Num [4 ]

Result [ 9 ] 7 + 2

Count [ 1 ] 2 - 1

Count: 1

Count = 1

1 > 0 ? => YES


Num [4 ]

Result [ 10] 9 + 1

Count [ 0 ] 1 - 1

C

oun

t: 0

Count = 0

0 > 0 ? => NO

Result: 10


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Page 1

AVRG (average, 1 , 5, )

Start

Stop

Rea

Pri t

average

Page 2

AVRG ( result, 1, 2, 3)

Retur

su = 1+ 2+ 3

result = su /3

Example:What is the output of the following flowchart when the input is N = 6

average

10

5

N=6

Sum = 10 + 5 + 6

average =21/3

Output:Average: 7

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