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Flow Charts

What are they good for?

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Purpose of Flow Charts

Visually show flow of data/process steps

within a system

Flow Charts Will

Define the problem
Show sequence of steps to solve problem
Show alternatives if problem is not solved

during the process

Usually created at beginning stages of a project
Used to facilitate communications between engineers and clients

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Today’s Topics

Flowchart Symbols
Structures
Sequence
Selection
Repetition

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Rules

Use Standard Symbols to show various types of

Decisions
Processes
Alternative paths (if statements/loops)
Input/Output

Basic Geometric Symbols

Start/End : Slots/Lozenges
Flow: Lines w/ Arrow End Markers
Processes: Rectangles
Input/Output: Parallelgram
Conditional/Decision: Rhombus

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	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

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	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

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Flow Chart Guidelines

In drawing a proper flow chart, all necessary requirements should be listed out in logical order.
The flowchart should be clear, neat and easy to follow. There should not be any room for ambiguity in understanding the flow chart.
The usual direction of the flow of a procedure or system is from left to right or top to bottom.
Only one flow line should come out from a process symbol.
Only one flow line should enter a decision symbol, but two or three flow lines, one for each possible answer, should leave the decision symbol.
Only one flow line is used in conjunction with terminal symbol.
Write within standard flow chart symbols briefly. As necessary, you can use the annotation symbol to describe data or computational steps more clearly.
If the flowchart becomes complex, it is better to use connector symbols to reduce the number of flow lines. Avoid the intersection of flow lines if you want to make it more effective and better way of communication.
Ensure that the flowchart has a logical start and finish.
It is useful to test the validity of the flowchart by passing through it with a simple test data.

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Basic Flow Charts

Linear Flow Chart

Decision Statements

Yes/No
# Times through a loop
Variable = specific value

Connecting flow between sheets

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Basic Flow Charts

Sub-Routines within a Program

Wait Statement (Pause)

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Making an Effective Flow Chart

Define the process boundaries with starting and ending points.
Complete the big picture before filling in the details.
Clearly define each step in the process. Be accurate and honest.
Identify time lags and non-value-adding steps.
Circulate the flowchart to other people involved in the process to get their comments.
Flowcharts don't work if they're not accurate or if the team is too far removed from the process itself. Team members should be true participants in the process and feel free to describe what really happens. A thorough flowchart should provide a clear view of how a process works. With a completed flowchart, you can:
Identify time lags and non-value-adding steps.
Identify responsibility for each step.
Brainstorm for problems in the process.
Determine major and minor inputs into the process with a cause & effect diagram.
Choose the most likely trouble spots with the consensus builder.

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Flow Chart: Student Assignment Submission

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Sequence

In 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 1

process 2

…

process n

In a flowchart,

sequence is expressed as:

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Function

Page 1

Page 2

End terminal

must be a “Return”

Start terminal for a

Function 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 what

to do. How to do it,

it comes later.

This part is known as

Function-Call

Body of a function is

the same with

normal flowchart

This flowchart calculates the average of three numbers

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Connectors on the same page

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

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Example:

Input:

Length <- 5

Width <- 3

Process:

Area = 5 * 3 = 15

Process:

Perimeter =

2* (5+3) = 16

Output

Area: 15

Perimeter: 16

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Selection is used in a computer program or algorithm �to determine which particular step or set of steps is to be executed

Binary Selection

In pseudocode, binary selection is expressed in the following ways:

IF condition THEN

process 1

ENDIF

IF condition THEN

process 1

ELSE

process 2

ENDIF

Binary Selection

In flowcharts, binary selection is expressed in the following ways:

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Selection�Binary (structure)

Binary Selection

In pseudocode, binary selection is expressed in the following ways:

IF condition THEN

process 1

ENDIF

IF condition THEN

process 1

ELSE

process 2

ENDIF

Binary Selection

In flowcharts, binary selection is expressed in the following ways:

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Repetition

Repetition allows for a portion of an algorithm or computer program

to 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

at the beginning and is known as a pre-test loop or
at the end of the loop and is known as a post-test loop.

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Repetition�Pre-test (structure)

Repetition: Pre-Test

A 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 true

process(es)

ENDWHILE

Repetition

In flowcharting

pre-test repetition

is expressed as:

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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:

REPEAT

process

UNTIL condition is true

Repetition

In a flowchart

post-test repetition

is expressed as:

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Repetition Pre-test (example)

An Example Using Pre-Test Repetition

Problem: Determine a safety procedure for travelling in a carriage on a moving train.

Pre-test Repetition

Pseudocode

WHILE the train is moving

keep wholly within the carriage

ENDWHILE

Pre-test Repetition

Flowchart

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Repetition Post-test (example)

An Example Using Post-Test Repetition

Problem: Determine a procedure to beat egg whites until fluffy.

Post-test Repetition

Pseudocode

REPEAT

beat the egg whites

UNTIL fluffy

Post-test Repetition

Flowchart

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Comments or description

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Selection�Binary (flowchart structure)

Note: In a flowchart it is most important to indicate

which path is to be followed when the condition is true, and
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.

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

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Selection�Binary (examples)

Selection is used in a computer program or algorithm

to determine which particular step or set of steps is to be executed.

Examples Using Binary Selection

Problem 1: Write a set of instructions to describe when to answer the phone.

Binary Selection

Pseudocode

IF the telephone is ringing THEN

answer the telephone

ENDIF

Binary Selection

Flowchart

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Selection�Binary (examples)

Examples Using Binary Selection

Problem 2: Write a set of instructions to follow when approaching a set of traffic control lights.

Binary Selection

Pseudocode

IF the signal is green THEN

proceed through the intersection

ELSE

stop the vehicle

ENDIF

Binary Selection

Flowchart

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Selection�Multi-way (structure)

Multi-way Selection

In pseudocode, multiple selection is expressed as:

CASEWHERE expression evaluates to

choice a : process a

choice b : process b

. .

OTHERWISE : default process

ENDCASE

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:

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Selection�Multi-way (examples)

Example Using Multi-way Selection

Problem: Write a set of instructions that describes how to:

respond to all possible signals at a set of traffic control lights.

Multi-way Selection

Pseudocode

CASEWHERE signal is

red : stop the vehicle

amber : stop the vehicle

green : proceed through the intersection

OTHERWISE : proceed with caution

ENDCASE

Multi-way Selection

Flowchart

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Example:

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

Num = 10

10 > 0 ? => YES

Input:

Num <- 10

Enter a Number >> 10

Output:

“Category A”

Category A

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Example:

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

Num = 0

0 > 0 ? => NO

Output:

“Category B”

Input:

Num <- 0

Enter a Number >> 0

Category B

Output:

“Category A”

Category A

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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 = 4

4 > 0 ? => YES

Variables (in memory):

Num [ 4 ]

Result [ 0 ]

Count [ 4 ]

Count: 4

Variables (in memory):

Num [ 4 ]

Result [ 4 ] 0 + 4

Count [ 3 ] 4 - 1

Count: 3

Count = 3

3 > 0 ? => YES

Variables (in memory):

Num [ 4 ]

Result [ 7 ] 4 + 3

Count [ 2 ] 3 - 1

Count: 2

Count = 2

2 > 0 ? => YES

Variables (in memory):

Num [ 4 ]

Result [ 9 ] 7 + 2

Count [ 1 ] 2 - 1

Count: 1

Count = 1

1 > 0 ? => YES

Variables (in memory):

Num [ 4 ]

Result [ 10] 9 + 1

Count [ 0 ] 1 - 1

Count: 0

Count = 0

0 > 0 ? => NO

Result: 10

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Page 1

Page 2

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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Quiz

What is a flowchart?
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.

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Assignment

Demo: Flow Chart: Number Factorial
Student Flow Chart Project

Program 1: Loop/Repetition

User Inputs x number of values

Exit when user types in 0 (zero)

Program adds numbers together
Output Average of User input

Program 2: Selections
Create a flowchart that takes 4 marks from the user, calculates and outputs the average and then� tells the user their letter grade based on the following guidelines: A = 80-100, B = 70-79.9, C = 60-69.9, D = 50-59.9, F < 50.

Program 3: Choice Flowchart

Pick an every day activity �I.E baking/cooking, getting ready in the morning, sports practice, etc.