introduction of flowchart 3664210
TRANSCRIPT
Introduction To Flowcharting
Today’s Topics
• Flowchart Symbols• Structures•Sequence•Selection•Repetition
Flowchart:
Represents an algorithm in graphical symbols
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.
Flowchart Symbols
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
Comments or descriptionStart
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
FunctionPage 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
The main flowcharting structures
1.Sequence2.Selection3.Repetition
A flowchart expressing the solution to an involved problem may have:
1.the main program flowchart on one page
2.with subprograms continuing the problem solution on subsequent pages.
Each of the five acceptable structures can be built from the basic elements
as shown below.
Each of the five acceptable structures can be built from the basic elements
as shown below.
Each of the five acceptable structures can be built from the basic elements
as shown below.
SequenceIn a computer program or an algorithm,
sequence involves simple steps which are to be executed one after the other.
The steps are executed in the same order in which they are written.
In pseudocode, sequence is expressed as:
process 1process 2……process n
In a flowchart, sequence is expressed as:
SequenceAn Example Using Sequence
Problem: Write a set of instructions that describe how to make a pot of tea.
Pseudocode
BEGINfill a kettle with waterboil the water in the kettleput the tea leaves in the potpour boiling water in the pot
END
Flowchart
Binary Selection
In pseudocode, binary selection is expressed in the following ways:
1. IF condition THENprocess 1
ENDIF
2. IF condition THENprocess 1
ELSEprocess 2
ENDIF
Binary Selection
In flowcharts, binary selection is expressed in the following ways:
Selection is used in a computer program or algorithm
to determine which particular step or set of steps is to be executed
SelectionBinary (structure)
Binary Selection
In pseudocode, binary selection is expressed in the following ways:
1. IF condition THENprocess 1
ENDIF
2. IF condition THENprocess 1
ELSEprocess 2
ENDIF
Binary Selection
In flowcharts, binary selection is expressed in the following ways:
SelectionBinary (flowchart structure)
Note: In a flowchart it is most important to indicate 1. which path is to be followed when the condition is true, and 2. which path to follow when the condition is false.
Without these indications the flowchart is open to more than one interpretation.
Note: There are two acceptable ways to represent a decision in all of the structures.Either method is acceptable. For consistency, the method 1 is used throughout this document.
1. The condition is expressed as a statement and the two possible outcomes are indicated by
• True• False
2. The condition is expressed as a question and the two possible outcomes are indicated by
• Yes• No
SelectionBinary (examples)
Examples Using Binary SelectionProblem 1: Write a set of instructions to describe when to answer the phone.
Binary SelectionPseudocode
IF the telephone is ringing THEN
answer the telephone
ENDIF
Binary SelectionFlowchart
SelectionBinary (examples)
Examples Using Binary SelectionProblem 2: Write a set of instructions to follow when approaching a set of traffic control lights.
Binary SelectionPseudocode
IF the signal is green THEN
proceed through the intersection
ELSEstop the vehicle
ENDIF
Binary SelectionFlowchart
SelectionMulti-way (structure)
Multi-way Selection
In pseudocode, multiple selection is expressed as:
CASEWHERE expression evaluates to
choice a : process achoice b : process b . . . . . .
OTHERWISE : default processENDCASE
Note: As the flowchart version of the multi-way selection indicates, only one process on each pass is executed as a result of the implementation of the multi-way selection.
Multi-way Selection
In flowcharts, multi-way selection is expressed as:
SelectionMulti-way (examples)
Example Using Multi-way SelectionProblem: Write a set of instructions that describes how to:
respond to all possible signals at a set of traffic control lights.
Multi-way SelectionPseudocode
CASEWHERE signal isred : stop the vehicleamber : stop the vehiclegreen : proceed through the intersection
OTHERWISE : proceed with cautionENDCASE
Multi-way SelectionFlowchart
RepetitionRepetition allows for a portion of an algorithm or
computer programto be done any number of times
dependent on some condition being met. An occurrence of repetition is usually known as a loop.
An essential feature of repetition is that each loop has a termination condition
to stop the repetition, or the obvious outcome is that
the loop never completes execution (an infinite loop).
The termination condition can be checked or tested 1. at the beginning and is known as a pre-test
loop or2. at the end of the loop and is known as a post-
test loop.
Repetition Pre-test (structure)
Repetition: Pre-TestA pre-tested loop is so named because the condition has to be met at
the very beginning of the loop or the body of the loop is not executed.
This construct is often called a guarded loop. The body of the loop is executed repeatedly while the termination condition is true.Repetition
In pseudocode, pre-test repetition is expressed as:
WHILE condition is trueprocess(es)
ENDWHILE
Repetition
In flowcharting pre-test repetition is expressed as:
Repetition Post-test (structure)
Repetition: Post-Test• A post-tested loop executes the body of the loop before testing the
termination condition. • This construct is often referred to as an unguarded loop. • The body of the loop is repeatedly executed until the termination condition is
true.An important difference between a pre-test and post-test loop is that the statements of a post-test loop are executed at least once even if the condition is originally true, whereas the body of the pre-test loop may never be executed if the termination condition is originally true. A close look at the representations of the two loop types makes this point apparent.Repetition
In pseudocode, post-test repetition is expressed as:
REPEATprocess
UNTIL condition is true
Repetition
In a flowchartpost-test repetition is expressed as:
Repetition Pre-test (example)
An Example Using Pre-Test RepetitionProblem: Determine a safety procedure for travelling in a carriage on a moving train.
Pre-test RepetitionPseudocode
WHILE the train is moving
keep wholly within the carriage
ENDWHILE
Pre-test RepetitionFlowchart
Repetition Post-test (example)
An Example Using Post-Test RepetitionProblem: Determine a procedure to beat egg whites until fluffy.
Post-test RepetitionPseudocode
REPEATbeat the egg whites
UNTIL fluffy
Post-test RepetitionFlowchart
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: 15Perimeter: 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 [ ]
Variables (in memory):
Num [ 4 ]Result [ ]Count [ ]
Count = 44 > 0 ? => YES
Variables (in memory):
Num [ 4 ]Result [ 0 ]Count [ 4 ]
Count: 4
Variables (in memory):
Num [ 4 ]Result [ 4 ] 0 + 4Count [ 3 ] 4 - 1
Count: 3
Count = 33 > 0 ? => YES
Variables (in memory):
Num [ 4 ]Result [ 7 ] 4 + 3Count [ 2 ] 3 - 1
Count: 2
Count = 22 > 0 ? => YES
Variables (in memory):
Num [ 4 ]Result [ 9 ] 7 + 2Count [ 1 ] 2 - 1
Count: 1
Count = 11 > 0 ? => YES
Variables (in memory):
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
T. O. L
Quiz
1. What is a flowchart?2. It is used to connect remote
flowchart portion on the same page. One flow line enters and one flow line exits.
3-5. Control Structures of Flowchart.
