1. Algorithms
for
Program Design
1

2. Process Modelling
Process modelling is performed during the design
stage of developing a new system.
Data Flow Diagrams - show WHAT the new system
must be able to do.
Process Specification - provides details of HOW the
required functionality is achieved.
Various techniques used to clarify procedures
Structure Diagrams
Flow Charts
Pseudocode / Structured English
Provides the logical design for a computer algorithm
2

3. Start
Start
Flow Charts
Subtotal = 00
Subtotal = • Not to be confused with Data Flow Diagrams (DFDs)
VAT = 1.175
VAT = 1.175 Shows steps required to achieve the
correct outcome
Input: ItemPrice
Input: ItemPrice Flow charts provide a graphical
representation of an algorithm
Subtotal = Subtotal +
Subtotal = Subtotal + • Can become complex and hard to follow
ItemPrice
ItemPrice • Best used to give overview of functionality.
Pseudocode provides a non-technical
no
End of Item list?
End of Item list? description of an algorithm
• More detailed and closely related to
yes programming code
Total = Subtotal **VAT
Total = Subtotal VAT Structure diagrams are useful to show a
hierarchical overview of program modules
Output:
Output: • Helps to identify how the main project
“Total Price = £” (Total)
“Total Price = £” (Total) components will be created
• Input - Processing - Output
Stop
Stop
3

4. Pseudocode
Pseudocode is a technique used during the design
stage of developing a program.
Used to translate the users requirements into a into a
complete sequence of unambiguous, logical steps.
It is written in Structured English to describe the
system operations accurately and precisely,
including all the steps need to code the program.
Can be understood by any programmer & coded into
any language.
4

5. How to….Create an Algorithm
Start with a statement of the user’s needs
Then write a program specification
Then write out in sentences what the
program needs to do at each step
All of the time, consider how a computer runs
an event driven program
INPUT – PROCESS – OUTPUT
5

6. How to ... Pseudocode
Starting with general sentences (Structured English)
Remove as many of the extra words as you can - just
leave the bare minimum
If values are being entered - input:
use the term “read in” or “get”…..
For any processing or calculations
use the logical operators + - * / < > = “True”, “False”
If results are being displayed - output:
use the term “print”
The final pseudocode should be language independent,
but must avoid any ambiguity.
6

7. Example:
Description of the stages of a program for
adding two numbers and displaying the result:
The user types in Number1
The user types in Number2
The program adds Number1 and Number2
The program displays the Total on the screen
This isn’t written in pseudocode quite yet……
7

8. Example:
Read in Number1
Read in Number2
Total = Number1 + Number2
Print (Total)
Now this is like program code
Because of this it is called pseudocode
Structured English is what it is written in
8

9. Example: Verify Product
9

10. Example: Verify Product
For each Ordered Product
Get Product(CatNo), Ordered(CatNo)
If Product(CatNo) = Ordered (CatNo) Then
Get Product (Level), Ordered (Quantity),
If Product (Level) >= Ordered (Quantity) Then
Order accepted = True
Else
Order accepted = False
End If
Else
Print Invalid Product No
End If
Next Product
Print confirmed order
10

11. Example: HND course
11

12. Example: Credit Card Authorisation
START Bank connection
GET Total due, Card type, Card number, Expiry date
GET Stolen cards list
IF Stolen = True THEN
Print “Retain card and destroy”
ELSE
LOOP WHILE Counter < 3 AND PIN = False
Increment Counter
GET PIN
IF PIN = True THEN
GET Limit, Balance
IF Total Due < Limit - Balance THEN
GET Ref (Transaction)
Balance = Balance + Total Due
PRINT “Transaction authorised” & Ref
ELSE Authorised = False
PRINT “Insufficient funds available”
END IF
EXIT Bank connection
END IF
END LOOP
PRINT “Incorrect PIN - Retain card and refer to bank”
END IF
EXIT Bank connection
12