1. Faculty of Computer Science & Information System
Introduction To
Flowcharting by
Jumail Bin Taliba
Faculty of Computer Science & Information System

2. Today’s Topics
Flowchart Symbols
Control Structures
Some examples

3. Flowchart:
Represents an algorithm in graphical symbols
Example: Algorithm for multiplying two numbers

4. Flowchart 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.
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.

5. Example: Process Output Start Terminal. Program starts here Input.
Enter values for
A and B
Process
Output
Stop Terminal
Program ends
here

6. Comments or description

7. Connectors on the same page
1- connection on the same flowchart portion
2- connection on the different flowchart portion

8. Connectors on a different page

9. Function The detail of how the function works
is put in another flowchart.
This is known as Function-Definition
Function
Page 1
Start terminal for a
Function is different.
Do not use “Start”
Page 2
Body of a function is
the same with
normal flowchart
At this point,
we only focus on what
to do. How to do it,
it comes later.
This part is known as
Function-Call
End terminal
must be a “Return”
This flowchart calculates the average of three numbers

10. Related terms and concepts
Parameters used in a function-definition
are called formal parameters
R, a, b, c are formal parameters
Related terms and concepts
Page 1
Page 2
AVRG is the function name
Objects enclosed by ( ) – result,
n1, n2, n3 - are called 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 be
different from its formal parameter
Parameters used in a function-call
are called actual parameters
result, n1, n2, n3 are actual parameters
This flowchart calculates the average of three numbers

11. Related terms and concepts (cont.)
In a function-definition, you should only
use formal parameters – R, a, b, c
You shouldn’t use actual parameters
Page 1
Page 2
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.

12. Related terms and concepts (cont.)
Page 1
Page 2
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 may be
called more than once
This flowchart calculates the average of three numbers

13. A function parameter may act as: Input
Related terms and concepts (cont.)
A function parameter may act as:
Input
Data of the function
Output
The result of the function
Both

14. Related terms and concepts (cont.)
Function definition:
R is the output parameter
a, b, c are input parameters
Related terms and concepts (cont.)
Page 1
Page 2
Function call:
result is the output
parameter.
n1, n2, n3 are the input
parameters.
This flowchart calculates the average of three numbers

15. Related terms and concepts (cont.)
Function definition:
x and y act as both input and output
parameters
Related terms and concepts (cont.)
Page 1
Page 2
Function call:
p and q act as both input and output
parameters.
This flowchart exchanges or swaps the value
of x and y each other

16. Related terms and concepts (cont.)
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:
Since it has only one output, the output is “RETURN”
Page 2
Page 2
The output parameter (R)
is removed from the formal
parameter list
and the result
is return

17. Related terms and concepts (cont.)
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
Page 1
Now, result is not
anymore a parameter
of the function-call

18. 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

19.  Sequential Structure Multiple statements considered as one statement
A statement means
a command or an instruction
statement
statement 
statement

20. If set condition is true, execute the statement, else do nothing
Selection Structure If
(one-choice)
“do it or don’t” 
statement
condition
condition
TRUE
FALSE
statement
If set condition is true, execute the statement, else do nothing

21. If-else (two-choices)
Selection Structure (cont..)
If-else (two-choices)
“do this one or
the other one”
TRUE
condition
condition
FALSE 
statement
Statement 1
Statement 2
If set condition is true, execute the first statement, else execute second statement

22. Nested if (if within if)
Selection Structure (cont..)
Nested if (if within if)
test1
test2
statement
FALSE
TRUE
test1
FALSE
TRUE
it is an “one-choice” if
Considered as one statement 

23. Complex if-else & if Statements
Selection Structure (cont..)
Complex if-else & if Statements x
FALSE
condition
TRUE
statement
TRUE
statement
condition
FALSE
statement
Considered as one statement

24.  ° Repetition Structure while Loop It is a pre-test loop
condition
body of loop
condition
FALSE
statement 
TRUE
While a set condition is true, repeat statement (body of loop)

25. do-while Loop It is a post-test loop
Repetition Structure (cont…)
do-while Loop It is a post-test loop
statement
statement 
condition
TRUE
FALSE
Do the statement (body of loop) while a condition is true

26. for Loop It is a pre-test loop
Repetition Control Structure (cont…)
for Loop It is a pre-test loop x
initialization
FALSE
condition
TRUE
body of loop
increment y

27. Example: Output Area: 15 Perimeter: 16 Input: Length <- 5
Width <- 3
Process:
Area = 5 * 3 = 15
Process:
Perimeter =
2* (5+3) = 16
Output
Area: 15
Perimeter: 16

28. Example:
What is the output of the following flowchart when the input Num= 10
Input:
Num <- 10
Enter a Number >> 10
Category A
Num = 10
10 > 0 ? => YES
Output:
“Category A”

29. Example:
What is the output of the following flowchart when the input is Num= 0
Input:
Num <- 0
Enter a Number >> 0
Category B
Category A
Num = 0
0 > 0 ? => NO
Output:
“Category B”
Output:
“Category A”

30. Variables (in memory): Variables (in memory): Variables (in memory):
Example:
What is the output of the following flowchart when the input is Num= 4
Variables (in memory):
Num [ 4 ]
Result [ ]
Count [ ]
Variables (in memory):
Num [ ]
Result [ ]
Count [ ]
Variables (in memory):
Num [ 4 ]
Result [ 4 ] 0 + 4
Count [ 3 ] 4 - 1
Variables (in memory):
Num [ 4 ]
Result [ 0 ]
Count [ 4 ]
Variables (in memory):
Num [ 4 ]
Result [ 7 ] 4 + 3
Count [ 2 ] 3 - 1
Variables (in memory):
Num [ 4 ]
Result [ 10] 9 + 1
Count [ 0 ] 1 - 1
Variables (in memory):
Num [ 4 ]
Result [ 9 ] 7 + 2
Count [ 1 ] 2 - 1
Input:
Num <- 4
Enter a Number => 4
Count = 4
4 > 0 ? => YES
Count = 3
3 > 0 ? => YES
Count = 2
2 > 0 ? => YES
Count: 4
Count = 0
0 > 0 ? => NO
Count = 1
1 > 0 ? => YES
Count: 3
Count: 2
Count: 1
Count: 0
Result: 10

31. Example:
What is the output of the following flowchart when the input is N = 6 10 5
average
Page 1
Page 2
N=6
Sum =
average =
21/3
Output:
Average: 7