1. Introduction to Pseudocode

2. What is Pseudocode? One of the popular representation of Algorithm
Widely choosen because:
easy to read and write
allow the programmer to concentrate on the logic of the problem
Structured in English language

3. Pseudocode Convention
Statement are written in simple English
Each instruction is written on a separate line
Keywords and indentation are used to signify particular control structures.
Each set of instructions is written from top to bottom, with only one entry and one exit.
Groups of statements may be formed into modules, and that group given a name.

4. Six Basic Computer Operations
A computer can receive information
Verb used:
Read  used when the algorithm is to receive the input from a record on a file
Get  used when the algorithm is to receive input from the keyboard.
Read student name
Get system date
Read number_1, number_2
Get tax_code

5. 2. A computer can put out information
Verb used:
Print  used when the output is to be sent to the printer
Write  used when the output is to be written to a file
Put, Output, Display  used when the output is to be written to the screen
Prompt  required before an input instruction Get, causes the message to be sent to the screen which requires the user responds, usually by providing input.
Print `Program Completed´
Write customer record to master file
Put out name, address and postcode
Output total_tax
Display ´End of data´
Prompt for student_mark
Get student_mark

6. 3. A computer can perform arithmetic
Verb used:
Compute
Calculate
Symbols used:
+, -, *, /, ()
Add number to total
Total = total + number
Divide total_marks by student_count
Sales_tax = cost_price * 0.10
Compute C = (F – 32) * 5/9

7. A computer can assign a value to a variable or memory location
Three cases :
To give data an initial value in pseudocode, the verbs Initialise or Set are used
To assign a value as a result of some processing, the symbols ´=´or ´´ are written
To keep a variable for later use, the verbs Save or Store are used.
Initialize total_price to zero
Set student_count to 0
Total_price = cost_price + sales_tax
Total_price  cost_price + sales_tax
Store customer_num in last_customer_num

8. A computer can compare two variables and select one of two alternate actions
Keyword used:
IF, THEN, ELSE
IF student_attendance_status is part_time THEN
add 1 to part_time_count
ELSE
Add 1 to full_time_count
ENDIF

9. 6. A computer can repeat a group of actions
Keyword used:
DOWHILE, ENDDO
DOWHILE student_total < 50
Read student record
Print student name, address to report
Add 1 to student_total
ENDDO

10. Meaningful names
When designing a solution algorithm, a programmer should introduce unique names, which are:
Represent the variables or objects in the problem
Meaningful
example: number1, number2, number3  more meaningful than A, B, C
Used word separator if more than one word
example: sales_tax, word_count
Or Capital letter as separator
example: salesTax, wordCount

11. The Structure Theorem
It is possible to write any computer program by using only three basic control structures that are easily represented in pseudocode:
Sequence
Selection
Repetition

12. Sequence Add 1 to pageCount Print heading line 1 Print heading line 2
Is the straightforward execution of one processing step after another.
Statement a
Statement b
Statement c
Add 1 to pageCount
Print heading line 1
Print heading line 2
Set lineCount to zero
Read customer record

13. Selection IF condition p is true THEN ELSE statement(s) in false case
Presentation of condition and the choice between two actions
IF condition p is true THEN
statement(s) in true case
ELSE
statement(s) in false case
ENDIF
Example:
IF student_attendance_status is part_time THEN
add 1 to part_time_count
ELSE
add 1 to full_time_count
ENDI>f

14. Repetition DOWHILE condition p is true statement block ENDDO
The presentation of a set of instructions to be performed repeatedly,
as long as a condition is true
DOWHILE condition p is true
statement block
ENDDO
Example:
Set student_total to zero
DOWHILE student_total < 50
Read student record
Print student name, address to report
Add 1 to student_total
ENDDO

15. DESIGNING A SOLUTION ALGORITHM
The most challengin task in the life cycle of a program
First attempt usually doesnt result in a finished product
Keep altering the step and algorithms till satesfied result achieved.

16. Point to be considered in Solution Algorithm
A name should be given to the algorithm, which is describe the function of algorithm
An END statement used to indicate the algorithm is complete
All processing steps between the algorithm name and END statement should be indented for readability.
Each processing step in the defining diagram relates directly to one or more statements in the algorithm.

17. Example 3.1. Solution Algorithm for example 2.1
A program is required to read three numbers, add them together and print their total.

18. Defining diagram
Input
Processing
Output
Number1
Number2
Number3
total

19. Solution Algorithm Add_three_numbers END
Read number1, number2, number3
Total = number1 + number2 + number3
Print total
END

20. Example 3. 2. Find average temperature
A program is required to prompt the terminal operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display to the screen the average temperature, calculated by (maximum temperature + minimum temperature)/2.

21. Defining diagram Input Processing Output Max_temp Min_temp
Prompt for temperatures
Get temperatures
Calculate average temperature
Display average temperature
Avg_temp

22. Solution Algorithm Find average_temperature
Prompt operator for max_temp, min_temp
Get max_temp, min_temp
Avg_temp= (max_Temp + min_temp)/2
Output avg_temp to the screen
END

23. What about this ? - Compute mowing time
A program is required to read from the screen the lenght and widht of a rectangular house block, and the lenght and width of the rectangular house that has been built on the block. The algorithm should then compute and display the mowing time required to cut the grass around the house, at the rate of two square metres per minute.

24. Solution Algorithm Calculate_mowing_time END
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght*block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=house_lenght*house_width
Mowing_area=block_area-house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END

25. Checking the solution algorithm (Desk Checking)
Tracing through the logic of the algorithm with some chosen data..

26. Step in desk Checking an algorithm
Choose valid simple input test case (2-3 enough)
Establish what the expected result should be.
Make a table of relevant variable names
Checking the test case line by line, step by step
Repeat process 4 for other test case
Check if expected result 2 matches with actual result 5

27. Example 3.4. Desk Chek for example 2.1
A program is required to read three numbers, add them together and print their total.

28. Solution Algorithm Add_three_numbers END
Read number1, number2, number3
Total = number1 + number2 + number3
Print total
END

29. Desk Checking Choose two sets input test data.
Set 1: 10,20, 30 and Set 2: 40, 41, 42
Data Set 1
Data Set 2
Number 1 10 40
Number 2 20 41
Number 3 30 42

30. 2. Establish the expected result for each test case
Data Set 1
Data Set 2
Total 60
123

31. 3. Set up a table of relevant variable names, and pass each test data set statement by statement.
Statement number
number1
number2
number3
total
First Pass 1 10 20 30 2 60 3
Print
Second Pass 40 41 42
123

32. 4. Check the expected results (60 and 123) match the actual results.

33. Desk Check of Example 3. 2.
A program is required to prompt the terminal operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display to the screen the average temperature, calculated by (maximum temperature + minimum temperature)/2.

34. Solution Algorithm Find average_temperature
Prompt operator for max_temp, min_temp
Get max_temp, min_temp
Avg_temp= (max_Temp + min_temp)/2
Output avg_temp to the screen
END

35. Desk Checking Choose two sets input test data.
Set 1: 30, 10 and Set 2: 40, 20
Data Set 1
Data Set 2
Max_temp 30 40
Min_temp 10 20

36. 2. Establish the expected result for each test case
Data Set 1
Data Set 2
Avg_temp 20 30

37. 3. Set up a table of relevant variable names, and pass each test data set statement by statement.
Statement number
Max_temp
Min_temp
Avg_temp
First Pass
1,2 30 10 3 20 4
0utput
Second Pass 40
output

38. 4. Check the expected results match the actual results.

39. Assignment 2: Desk Checking for Compute mowing time
A program is required to read from the screen the lenght and widht of a rectangular house block, and the lenght and width of the rectangular house that has been built on the block. The algorithm should then compute and display the mowing time required to cut the grass around the house, at the rate of two square metres per minute.

40. Solution Algorithm Calculate_mowing_time END
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght*block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=house_lenght*house_width
Mowing_area=block_area-house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END

41. Calculate_mowing_time
Assignment 3 – Desk Checking for Mowing_time which now contains a logic error
Calculate_mowing_time
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght * block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=block_lenght * block_width
Mowing_area=block_area - house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END

42. Rule of Assignment Submission
Submit at the latest one day before the following class begin.
Submission after the time will be considered as delay and affect the mark.
Use a combination of your name and assignment number as file name.
For example: BasnendarE_Assigment1.doc