meljun cortes algorithm by flowcharting

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

Introduction To Flowcharting

MELJUN CORTES


Today’s Topics

• Flowchart Symbols• Control Structures• Some examples


Flowchart:

Represents an algorithm in graphical symbols

Example: Algorithm for multiplying two numbers

Start

Stop

Get AGet B

Display theResult C

Calculate ResutC=A*B


Terminal: Used to indicates the start and end of a flowchart. 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. One flow line enters and one flow line exits.

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

Decision: Used to represent operations in which there are two 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 flowchart portion on the same page. One flow line enters and one flow line exits.

Off-page Connector: Used to connect remote flowchart portion 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 of control.

Flowchart Symbols


Example:

Start

Stop

Read ARead B

Display theResult C

Calculate ResutC=A*B

Start Terminal. Program starts here

Stop TerminalProgram ends here

Input.Enter values for A and B

Process

Output


Comments or description

Start

Read N, M

No

Yes

Stop

N = The number of studentsM = The number of subjects


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


Connectors on a different page

Page 1 Page 2

Start

No

1

Yes 1

2

Stop

2


Function

Page 1

AVRG (result, n1, n2,n3)

Start

Stop

Readn1, n2 , n3

Printresult

Page 2

AVRG ( result,n1, n2,n3)

Return

sum = n1+ n2+n3

result = sum/3

End terminal must be a “Return”

Start terminal for aFunction is different.Do not use “Start”

The detail of how the function works is 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 is the same with normal flowchart

This flowchart calculates the average of three numbers


Related terms and concepts

Page 1


Start

Stop

Readn1, n2 , n3

Printresult

Page 2

AVRG ( R, a, b,c)

Return

sum = a+ b+c

R = sum/3

AVRG is the function name

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

Parameters used in a function-callare 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 represents an actual parameter according to 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



Related terms and concepts (cont.)

Page 1


Start

Stop

Readn1, n2 , n3

PrintR

Page 2

AVRG ( R, a, b,c)

Return

sum = n1 + n2 + n3

R = sum/3

In a function-definition, you should only use formal parameters – R, a, b, c

You shouldn’t 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.


Page 1

AVRG (average1, n1, n2,n3)

Start

Stop

Readn1, n2 , n3

Printresult

Readn4, n5 , n6

AVRG (average2, n4, n5, n6)

result = (average1 +average2) / 2


Page 2

AVRG ( R, a, b,c)

Return

sum = a+ b+c

R = sum/3

A function may be called more than once

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

When comes to this:R represents average2,a represents n4,b represents n5,c represents n6




A function parameter may act as:

• InputData of the function

• OutputThe result of the function

• Both


Page 1


Start

Stop

Readn1, n2 , n3

Printresult

Page 2

AVRG ( R, a, b,c)

Return

sum = a+ b+c

R = sum/3

Function call:

result is the output parameter. n1, n2, n3 are the input parameters.

Function definition:

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





Page 1 Page 2

EXCHG( x, y)

Return

hold = x

x = y

y = hold

Start

Stop

Printp, q

EXCHG (p, q)

Readp, q

Function call:

p and q act as both input and output parameters.

Function definition:

x and y act as both input and output parameters

This flowchart exchanges or swaps the value of x and y each other


Page 2

AVRG ( R, a, b,c)

Return

sum = a+ b+c

R = sum/3


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

AVRG ( a, b,c)

Return R

sum = a+ b+c

R = sum/3

Since it has only one output, the output is “RETURN”

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

and the result is return



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


Start

Stop

Readn1, n2 , n3

Printresult

Page 1

result =AVRG (n1, n2, n3)

Start

Stop

Readn1, n2 , n3

Printresult

Now, result is notanymore a parameterof the function-call


Control Structure

• Describe the flow of execution.• In flowcharts, flow of execution is represented by the arrow line.

• Types of control structure:•Sequential•Selection•Repetition


Sequential Structure

statement

statement

statement

Multiple statements considered as one statement

A statement means a command or an instruction


Selection Structure

If

(one-choice)

condition

statement

°

TRUE

FALSE statement

If set condition is true, execute the statement, else do nothing

“do it or don’t”

condition


Selection Structure (cont..)If-else

(two-choices)

condition

Statement 2Statement 1

°

statement

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

TRUE FALSE

“do this one or the other one”

condition


Considered as one

statement

Nested if (if within if)

Selection Structure (cont..)

test1

test2

statement

°

°FALSE

FALSE

TRUE

TRUE

test1

°

°

FALSE

TRUE

it is an “one-choice” if


Complex if-else & if Statements

°

x

condition

statement

condition

statement

°

statement TRUE

TRUE

FALSE

FALSE

Considered as one statement

Selection Structure (cont..)


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


Repetition Structure (cont…)do-while Loop

It is a post-test loop

statement

FALSETRUE

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

statement

°

condition


for Loop

It is a pre-test loop

x

initialization

°condition

body of loop

increment

y

FALSE

TRUE

Repetition Control Structure (cont…)


Example:

Start

Stop

ReadLength,Width

PrintArea,

Perimeter

Calculate AreaArea=Length * Width

Calculate PerimeterPerimeter=

2 * (Width+Length)

Input:Length <- 5Width <- 3

Process:Area = 5 * 3 = 15

Process:Perimeter = 2* (5+3) = 16

Output

Area: 15

Perimeter: 16


Start

Stop

Read Num

Print"Category A"

Yes

Num>0? No

Print"Category B"

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

Num = 1010 > 0 ? => YES

Input:Num <- 10

Enter a Number >> 10

Output:“Category A”

Category A


Start

Stop

Read Num

Print"Category A"

Yes

Num>0? No

Print"Category B"

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

Num = 00 > 0 ? => NO

Output:“Category B”

Input:Num <- 0

Enter a Number >> 0

Category B

Output:“Category A”

Category A


Start

Stop

PrintResult

Result=Result + Count

Count=Count - 1

Initialize

Result=0Count=Num

Count>0?

Read Num

No

Print Count

Yes

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

Input:Num <- 4

Enter a Number => 4

Variables (in memory):

Num [ ]Result [ ]Count [ ]


Num [ 4 ]Result [ ]Count [ ]

Count = 44 > 0 ? => YES


Num [ 4 ]Result [ 0 ]Count [ 4 ]

Count: 4


Num [ 4 ]Result [ 4 ] 0 + 4Count [ 3 ] 4 - 1

Count: 3

Count = 33 > 0 ? => YES


Num [ 4 ]Result [ 7 ] 4 + 3Count [ 2 ] 3 - 1

Count: 2

Count = 22 > 0 ? => YES


Num [ 4 ]Result [ 9 ] 7 + 2Count [ 1 ] 2 - 1

Count: 1

Count = 11 > 0 ? => YES


Num [ 4 ]Result [ 10] 9 + 1Count [ 0 ] 1 - 1

Count: 0

Count = 00 > 0 ? => NO

Result: 10


Page 1

AVRG (average, 10, 5, N)

Start

Stop

ReadN

Printaverage

Page 2

AVRG ( result,n1, n2,n3)

Return

sum = n1+ n2+n3

result = sum/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

meljun cortes algorithm by flowcharting

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