1. Decision Tables and Pseudocode
Rizwan Rehman
Asstt. Professor
Centre for Computer Studies

2. Decision Tables - General
Decision tables are a precise yet compact way to model complicated logic. Decision tables, like if-then-else and switch-case statements, associate conditions with actions to perform. But, unlike the control structures found in traditional programming languages, decision tables can associate many independent conditions with several actions in an elegant way.

3. Decision Tables - Usage
Decision tables make it easier to observe that all possible conditions are accounted for.
Decision tables can be used for:
Specifying complex program logic
Generating test cases (Also known as logic-based testing)
Logic-based testing is considered as:
structural testing when applied to structure (i.e. control flow graph of an implementation).
functional testing when applied to a specification.

4. Decision Tables - Structure
Conditions - (Condition stub)
Condition Alternatives – (Condition Entry)
Actions – (Action Stub)
Action Entries
Each condition corresponds to a variable, relation or predicate
Possible values for conditions are listed among the condition
alternatives
Boolean values (True / False) – Limited Entry Decision Tables
Several values – Extended Entry Decision Tables
Don’t care value
Each action is a procedure or operation to perform
The entries specify whether (or in what order) the action is to be
performed

5. To express the program logic we can use a limited-entry decision table consisting of 4 areas called the condition stub, condition entry, action stub and the action entry:
Condition entry
Rule1
Rule2
Rule3
Rule4
Condition1
Yes No
Condition2 X
Condition3
Condition4
Action1
Action2
Action3
Condition
stub
Action stub
Action Entry

6. We can specify default rules to indicate the action to be taken when none of the other rules apply.
When using decision tables as a test tool, default rules and their associated predicates must be explicitly provided.
Rule5
Rule6
Rule7
Rule8
Condition1 X No
Yes
Condition2
Condition3
Condition4
Default action

7. Decision Table - Example
Conditions
Printer does not print Y N
A red light is flashing
Printer is unrecognized
Actions
Heck the power cable X
Check the printer-computer cable
Ensure printer software is installed
Check/replace ink
Check for paper jam
Printer Troubleshooting

8. Pseudocode

9. Flowcharts were the first design tool to be widely used, but unfortunately they do not reflect some of the concepts of structured programming very well.
Pseudocode, on the other hand, is a newer tool and has features that make it more reflective of the structured concepts. The drawback is that the narrative presentation is not as easy to understand and/or follow.

10. Rules for Pseudocode Write only one statement per line
Capitalize initial keyword
Indent to show hierarchy
End multiline structures
Keep statements language independent

11. One Statement Per Line
Each statement in pseudocode should express just one action for the computer. If the task list is properly drawn, then in most cases each task will correspond to one line of pseudocode.
Task List
Read name, hours worked, rate of pay
Perform calculations
gross = hours worked * rate of pay
Write name, hours worked, gross
Pseudocode
READ name, hoursWorked, payRate
gross = hoursWorked * payRate
WRITE name, hoursWorked, gross

12. Capitalize Initial Keyword
In the example below note the words: READ and WRITE. These are just a few of the keywords to use, others include:
READ, WRITE, IF, ELSE, ENDIF, WHILE, ENDWHILE
Pseudocode
READ name, hoursWorked, payRate
gross = hoursWorked * payRate
WRITE name, hoursWorked, gross

13. Indent to Show Hierarchy
Each design structure uses a particular indentation pattern
Sequence:
Keep statements in sequence all starting in the same column
Selection:
Indent statements that fall inside selection structure, but not the keywords that form the selection
Loop:
Indent statements that fall inside the loop but not keywords that form the loop
READ name, grossPay, taxes
IF taxes > 0
net = grossPay – taxes
ELSE
net = grossPay
ENDIF
WRITE name, net

14. End Multiline Structures
READ name, grossPay, taxes
IF taxes > 0
net = grossPay – taxes
ELSE
net = grossPay
ENDIF
WRITE name, net
See the IF/ELSE/ENDIF as constructed above, the ENDIF is in line with the IF. The same applies for WHILE/ENDWHILE etc…

15. Language Independence
Resist the urge to write in whatever language you are most comfortable with, in the long run you will save time. Remember you are describing a logic plan to develop a program, you are not programming!

16. The Selection Structure
amount < 100
yes no
interestRate = .06
interestRate = .10
IF amount < 100
interestRate = .06
ELSE
Interest Rate = .10
ENDIF
Pseudocode 

17. The Looping Structure
In flowcharting one of the more confusing things is to separate selection from looping. This is because each structure use the diamond as their control symbol. In pseudocode we avoid this by using specific keywords to designate looping
WHILE/ENDWHILE
REPEAT/UNTIL

18. WHILE / ENDWHILE count = 0 WHILE count < 10 ADD 1 to count
WRITE count
ENDWHILE
WRITE “The End”
Start
count = 0
count
<10
Mainline
count = 0
WHILE count < 10
DO Process
ENDWHILE
WRITE “The End”
Process
ADD 1 to count
WRITE count
 Modular
Write
“The End”
add 1 to
count
write count
Stop

19. REPEAT / UNTIL count = 0 REPEAT ADD 1 to count WRITE count
Start
count = 0
REPEAT
ADD 1 to count
WRITE count
UNTIL count >= 10
WRITE “The End”
count = 0
add 1 to
count
Mainline
count = 0
REPEAT
DO Process
UNTIL count >= 10
WRITE “The End”
Process
ADD 1 to count
WRITE count
 Modular
write count
count
<10
Write
“The End”
Stop

20. Advantages & Disadvantages
Flowchart Advantages:
Standardized
Visual
Pseudocode Advantages
Easily modified
Implements structured concepts
Done easily on Word Processor
Flowchart Disadvantages:
Hard to modify
Structured design elements not implemented
Special software required
Pseudocode Disadvantages:
Not visual
No accepted standard, varies from company to company

21. Thank You