1. CHAPTER 1
Introduction to Structured Programming

2. PROGRAMMING TERMINOLOGY
An activity consists of writing a program that will process the input data to produce the required output/document.
Input
(Set of Instructions)
Processing
INPUT
DATA
Output
(Report)

3. PROGRAM
written using a programming language, eg. C, Java, C++, BASIC etc.
Before writing code, it is very important to plan the solution to the problem – solution algorithm

4. SOLUTION ALGORITHM
A sequence of logic steps/instructions to the computer/people to perform a specific task
It is like a recipe : Step by step guide, that need to be followed in the right sequence
Properties:
Steps must be defined precisely (in detail) and clearly
Process must have an end – finite steps
The correct solution to an identified problem

5. ALGORITHM
Example : At a Public Phone
MAKE A CALL

6. ALGORITHM Steps are in correct order, performed from top to bottom.
Steps can be made up of combination of all control structures (sequence, selection, iteration)
Indentation is very important to show different control structures

7. ALGORITHM
Give an example of an algorithm of a daily activity e.g. watching a TV programme.
TASK : Write a solution algorithm to add 2 numbers and show the result.
1. Get first number
2. Get second number
3. Add first number and second number,
put the answer in sum
4. Display sum

8. ALGORITHM
TASK : Write a solution algorithm to find and display the average temperature. The maximum and minimum temperature readings are accepted as integers.
1. Get min_temp
2. Get max_temp
3. Calculate average
avg_temp = (min_temp + max_temp) / 2
4. Display avg_temp

9. GENERAL STEPS IN PROGRAM DEVELOPMENT
Define problem
Understand requirements
Determine input, output and processes
Outline solution
Break problem into smaller tasks or steps, draft solution
Develop outline to algorithm
Expand to precise steps – tasks and order
Test algorithm for correctness
Desk checking – walk through the logic of algorithm
Code the algorithm
Run on the computer
Using compiler and test data to check for errors
Document and maintain program

10. PROGRAM LIFE CYCLE aka Software/Program development cycle 9 Steps:
Problem specification
Problem analysis
Structured program design
Program coding
Program debugging
Program testing
Program installation
Program maintenance
Program documentation

11. (1) PROBLEM SPECIFICATION
Definition of problem by user to system analyst/programmer
This might include new user requirements
Need to be read carefully to understand completely the user requirements

12. Project Management

13. More Perceptions….

15. (2) PROBLEM ANALYSIS Includes : Initialization Input definition
Giving specific/initial value to variables eg. Total = 0
Input definition
Data to be fed into the computer – from keyboard/file
Output definition
layout of the output – screen/printer
Processing requirements
Solution algorithm/sequence of steps required to transform input to the required output
Processing controls
Validation checks on input for accurate processing
Program test plan
A range of test data to ensure the correctness of the program. This includes the calculation of expected result to verify the actual result produced.

16. (3) STRUCTURED PROG. DESIGN
Use of proper design techniques to illustrate the program specification in a systematic way
representing the tasks required in the program specification showing all input, processing and output requirements
Examples :
Top-down stepwise refinement method
Pseudocode
JSP

17. (4) PROGRAM CODING
Translation of design into programming language code e.g. C, C++, Pascal, QBasic
aka implementation

18. (5) PROGRAM DEBUGGING
The task of finding and removing errors/bugs from the program.
3 types of errors:
Syntax – error relating to the programming language used
Logical – error in programming logic
Run-time/execution – error during running/ execution of program

19. (6) PROGRAM TESTING
Is done using test data specified in the problem analysis.
Compiler is required to detect for Syntax and execution error, while specific test data to detect for logical error.
repeatedly done until program is running and producing the output as required
Less time required for testing if the program is well designed.

20. (7) PROGRAM INSTALLATION
Program is transferred to the user’s machine and made to work.
3 strategies:
The new program may run concurrently with the old one or
it may completely replaced the old one or
It may phased in gradually

21. (8) PROGRAM MAINTENANCE
Once the program is installed and operated, it will be monitored for some time to ensure that program is error-free.
Corrections will have to be made to the affected program/part of the program.

22. (9) PROGRAM DOCUMENTATION
All processes in all stages during the system development must be documented/written down.
This documentation is vital for future reference/for future maintenance of the program.

23. CHARACTERISTICS OF A GOOD PROGRAM
Correctness – fulfilling user requirements
Reliability – it produces correct output and validates input data to avoid program crash
Portability – easily installed from one machine to another with minimal modification
Maintainability – easily followed and modified, not only to the programmer who wrote it
Readability – clearly documented
Use of resources – fast in processing, uses minimum storage space and able to run on existing hardware.

24. STRUCTURED PROGRAMMING
A programming methodology for constructing hierarchically ordered modular programs using standardised control structures
Structured programming helps to write effective, error-free programs – new/modified.
There are many ways to solve a problem, but some are more desirable than others.
Original concepts was first published in by Bohm and Jacopini.
Designing of programs using a Structure Theorem which eliminating the GOTO statement and established a structured framework for representing solution.

25. STRUCTURED PROGRAMMING
Structure theorem is based on 3 control structures – sequence, selection and iteration.
Structured programming incorporates the concepts of stepwise refinement method and modular design.
Modular design groups tasks which perform the same function together e.g. printing of report headings, calculation etc.

26. Structured Techniques
Some of the techniques for program design:
Structured English
Flowcharts
Top-down stepwise refinement method
Jackson Structured Programming method
Pseudocode etc.

27. Problem specification
A program is required to take in 2 numbers as integers, then calculate and display the sum.

28. Structured English Example :
A method of specifying unambiguous narrative used to define procedural logic.
It lacks the precision of meaning and simplicity when programming.
Example :
Accept first integer and second integer
Add first integer and second integer and then put the result in sum
Display sum

29. Flow Chart
START
Sum := num1 + num2
Display sum
Get num1 & num2
END
Diagrams which show the sequence of steps to perform a specific programming task

30. Top-Down Stepwise Refinement Method
a process of developing a program by performing a sequence of refinement steps. First general solution is outlined and then is broken down into more detailed steps
Uses basic control structures :
sequence structure
selective structure
iterative structure

31. Top-Down Stepwise Refinement Method
Example :
Initialization
none
Input Definition
num1, num2
Output Definition
Sum = 999
Processing Requirements
Read num1, num2
Calculate
sum = num1 +num2
Display sum
Processing Control
Numbers must be integer

32. Top-Down Stepwise Refinement Method
num1
num2
sum 29 50 79 30
120
150
50.8 20
error
Test Data and Expected Result
Calculate Sum
Read num1
Read num2
Sum = num1 + num2
Print Sum
STRUCTURED CHART

33. Jackson Structured Program (JSP) Method
Uses the same principle of control structures but concentrates on both data structures and program structures
Combine the input/output data structures to form a program structure, identify the condition and Actions involved, produce the pseudocode and implement the pseudocode

34. Jackson Structured Program (JSP) Method
Input Data
num1
num2
Sum
Output
INPUT DATA STRUCTURE
OUTPUT DATA STRUCTURE

35. Jackson Structured Program (JSP) Method
Calculate Sum
num1
num2
Sum
PROGRAM STRUCTURE

36. Jackson Structured Program (JSP) Method
List of Conditions
none
List of Actions
Input Action
Read num1
Read num2
Output Action
Print sum
Computation
Sum = num1 + num2

37. Jackson Structured Program (JSP) Method
ALLOCATION OF ACTIONS
Calculate Sum
num1
num2
Sum 1 2
4,3

38. Pseudocode aka Schematic Logic
Represent the statements of algorithm in English which makes it easy to read and write and to convert it to the targeted programming language.
Translation stage between the program structure diagram and the program code
BEGIN PROCESS_SUM sequence
READ num1, num2;
sum = num1 + num2;
WRITE sum;
END PROCESS_SUM sequence
Example :

39. Pseudocode properties
Understandable to user
Hierarchically structured and using indentation to show this structure
Similar structure to the targeted programming code
Comments are clearly marked

40. Pseudocode rules Indentation Control structures are clear
sequence steps are placed on separate lines, each is ended with a semicolon. Continuation lines are indented if more than one line is required.
Use of keywords to show
the structures e.g IF, THEN, ELSE, WHILE etc
The logic e.g. AND, OR, NOT
Keywords may be selected to be independent of the language descriptions

41. Pseudocode rules
Block of instructions are grouped together having meaningful name to describe the function (modularization)
Keywords and names of blocks are in capital letters, others are not
Comments are delimited with a beginning asterisks and ends with semicolon
Use of parenthesis to show precedence of operations to avoid ambiguities
Make the end of a structure clear using ENDIF, ENDDO etc

42. Keywords KEYWORD DESCRIPTION PROCEDURE Starts a logical segment
ENDPROCEDURE
Terminates a logical segment
BEGIN
Starts a logical block within a segment
ENDBEGIN
Terminates a begin block
GET / READ
Input data
PUT / WRITE
Output data
IF…THEN
Conditional branch
IF…THEN…ELSE
Conditional branch (two ways)

43. Keywords KEYWORD DESCRIPTION ENDIF Terminates IF structure DO…WHILE
Repetitive block
DO…UNTIL
Repetitive block that will be executed at least once
DO…FROM…TO…BY
Incremental block
ENDDO
Terminates a block
CASEENTRY
Starts a multiple branch
ENDCASE
Terminates a CASE structure
CALL
Invocation of a subroutine

44. Problem specification Example 1
A program is required to read three numbers, add them together and print their total

45. Problem analysis INPUT PROCESS OUTPUT number1 number2 number3
Using IPO Chart (Input-Process-Output Chart)
INPUT
(nouns & adjectives)
PROCESS
(verbs & adverbs)
OUTPUT
number1
number2
number3
Read 3 numbers
Calculate total
Print total
total

46. Problem analysis (step-wise refinement method)
Initialization
none
Input Definition
number1 , number2, number3
Output Definition
The sum is =
Processing Requirements
Read number1, number2, number3
Calculate total
total = number1 + number2 + number3
Print total

47. Problem analysis (step-wise refinement method)
Processing Controls
none
Test Data and Expected Results
number1
number2
number3
total 40 50 60
150.0
10.5
20.2
30.8
61.5 10 20 -5
25.0

48. Variables
Variables/objects in the problem and the processing steps/program are referenced by names.
Names must be unique and short (max 25 letters) but meaningful
Names are used to identify a particular storage area in the memory.
Good Examples : number, sum, average, min, max.
Bad Examples: a, b, c, m1, x2

49. Problem specification Example 2
A program is required to read in the maximum and minimum temperatures on a particular day and calculate and print the average temperature

50. Problem analysis INPUT PROCESS OUTPUT Min_temp Max_temp
(nouns & adjectives)
PROCESS
(verbs & adverbs)
OUTPUT
Min_temp
Max_temp
Read max_temp, min_temp
Calculate average temp
Print average temp
avg_temp

51. Problem analysis (step-wise refinement method)
Initialization
none
Input Definition
max_temp, min_temp
Output Definition
Average Temperature =
Processing Requirements
Read max_temp, min_temp
Calculate average
avg_temp = (max_temp + min_temp) / 2
Print avg_temp

52. Problem analysis (step-wise refinement method)
Processing Controls
Temperatures cannot be negative values
Average temperature is rounded to 1 d.p.
Test Data and Expected Results
max_temp
min_temp
avg_temp 60 50
55.0 85
72.5 30
-10
error

53. Problem specification Example 3
Design a program to print the student number and grade given the student number and four test marks. The grade is based on the following rules :
average mark
grade
≥ 80
Distinction
≥ 65 and < 80
Merit
≥ 50 and < 65
Pass
< 50
Fail

54. Problem analysis INPUT PROCESS OUTPUT
Using IPO Chart (Input-Process-Output Chart)
INPUT
(nouns & adjectives)
PROCESS
(verbs & adverbs)
OUTPUT
studentNo
Test1
Test2
Test3
Test4
Read studentNo, test1, test2, test3, test4
Calculate average mark
Decide grade
Print studentNo, grade
grade

55. Problem analysis (step-wise refinement method)
Initialization
no_test = 4
Input Definition
studentNo, test1, test2, test3, test4
Output Definition
Student No : XXXXXX
Grade : XXXXXXXXX
Processing Requirements
Read studentNo, test1, test2, test3, test4
Calculate average
avg_mark = (test1 + test2 + test3 + test4) / no_test

56. Problem analysis (step-wise refinement method)
Processing Requirements (Cont..)
Decide Grade
If avg_mark >= 80
grade = “Distinction”
else
if avg_mark >= 65
grade = “Merit”
if avg_mark >= 50
grade = “Pass”
grade = “fail”
Print studentNo, grade

57. Problem analysis (step-wise refinement method)
Processing Controls
Test mark should be in the range of 0 to 100
Average mark must be integer.

58. Problem analysis (step-wise refinement method)
Test Data and Expected Results
studentNo
Test1
Test2
Test3
Test4
avg_mark
grade
Cp/01/21/01 90 80 85 86
Distinction
Cp/02/21/01 60 50 75 66
Merit
Cp/03/21/01 40 70 55
Pass
Cp/04/21/01 30 35
Fail
Cp/05/21/01
110
error
Cp/06/21/01
-70

59. Find the average of 10 integers which lie between 0 and 100 exclusive
Problem specification Example 4
Find the average of 10 integers which lie between 0 and 100 exclusive

60. Problem analysis INPUT PROCESS OUTPUT
Using IPO Chart (Input-Process-Output Chart)
INPUT
(nouns & adjectives)
PROCESS
(verbs & adverbs)
OUTPUT
number
(10 integers)
Read number
Calculate average
Print average
avg_num

61. Problem analysis (step-wise refinement method)
Initialization
total = 0 , num_count = 0
Input Definition
number
Output Definition
Average value =

62. Problem analysis (step-wise refinement method)
Processing Requirements
While num_count < 10
Read number
If number > 0 AND number <100
total = total + number
Add 1 to num_count
Calculate average
avg_num = total / num_count
Print avg_num

63. Problem analysis (step-wise refinement method)
Processing Controls
Number must be > 0 and < 100
Average is rounded off to 2 d.p.
Test Data and Expected Results
number
output
1,2,3,4,5….99
Print average
error
103