1. TEL 104 / MKK Fundamental Programming: Lecture 3

2. Assignment 1 Review:
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

3. Step 1
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.

4. Defining diagram Input Processing Output Block_lenght Block_width
House_lenght
House_width
Mowing_time

5. Step 2
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.

6. Defining diagram Input Processing Output Block_lenght Block_width
House_lenght
House_width
Prompt for block measurements
Get block measurements
Prompt for house measurements
Get house measurements
Calculate mowing area
Calculate mowing time
Mowing_time

7. Introdution to Program Data
Three main discussion:
Variables
Constants
Literals

8. Variables
Is the name given to a collection of memory cell, designed to store particular data item.
The value stored may change or vary as the program executes.
Example: variable total_amount  may contain several values during the execution of the program

9. Constant
Is a data item with a name and a value that remain the same during the execution of the program.
Example : name: ´´Fifty´´  given to a data item that contains the value 50

10. Literal
Is a constant whose name is the written representation of its value.
Example: the program may contain the literal `50`

11. Data Types Should be clearly defined at the beginning of the program.
Can be:
Elementary data items
Data structures

12. Elementary data items
Contain single variable that is always treated as a unit.
Usually classified into data types.
A data type consists of a set of data values and a set of operation that can be performed on those values.

13. Elementary data Items (cont)
The most common elementary data types:
Integer: representing a set of whole numbers, positive, negative or zero.
e.g. 3, 576, -5
Real : representing a set of numbers, positive or negative, which may include values before or after a decimal point. Sometimes referred to as floating point numbers.
e.g. 19.2, 1.92E+01,

14. The most common elementary data types: (cont)
Character: representing the set of characters on the keyboard, plus some special characters.
e.g. ´A´, `b`, ´$´
Boolean: representing a control flag or switch, which may contain one of only two possible values; true or false.

15. Data Structures Is an aggregate of other data items.
Its component could be elementary data items or another data structure.
Data is grouped together in a particular way to reflects the situation with which the program is concerned.

16. The most common Data Structures:
Record: a collection of data items or fields that all bear some relationship to one another.
example: a student record  may contain the student‘s number, name, address and enrolled subjects.
File: a collection of records.
example: a student file  may contain a collection of the above student records.

17. The most common Data Structures: (cont)
Array: a data structure that is made up of a number of variables or data items that all have the same data type and are accessed by the same name.
Example: an array called ´scores´ may contain a collection of students‘ exam scores.
Access to the individual items in the array is made by the use of an index or subscript beside the name of the array  scores[3]

18. The most common Data Structures: (cont)
String: a collection of characters that can be fixed or variable.
Example: the string ´Basnendar Eko´may represent a student‘s name.

19. Files A popular method to enter and store information.
Major advantage of using files are:
Several different program can access the same data
Data can be entered and reused several times.
Data can be easily updated and maintained.
The accuracy of the data is easier to enforce.

20. Files (cont) Two different methods of storing data on files:
Sequential or text files, where data is stored and retrieved sequentally  may be opened to read or to write, but not both operations on the same file.
Direct or random-access files, where data is stored and retrieved randomly, using a key or index  can be opened to read and write on the same file.

21. Data Validation
Data should always undergo a validation check before it is processed by a program.
Different types of data require different check – for example:
Correct type: the input data should match the data type definition stated at the beginning of the program.
Correct range: the input should be within a required set of values.
Correct lenght: the input data – for example, string – should be the correct length.
Completeness: all required fields should be present.
Correct date: an incoming data should be acceptable.

22. Introduction to Pseudocode

23. 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

24. 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.

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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.

37. 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.

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

39. Defining diagram
Input
Processing
Output
Number1
Number2
Number3
total

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

41. 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.

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

43. 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

44. 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.

45. 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

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

47. 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

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

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

50. 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

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

52. 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

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

54. 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.

55. 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

56. 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

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

58. 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

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

60. 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.

61. 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

62. 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

63. 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