This presentation looks at the fundamentals of program design and the use of the Sequence, Selection and Iteration constructs.

1. SECTION 2

2. STAGES OF PROGRAM DEVELOPMENT
 PROBLEM DEFINITION
 ANALYSIS
 DESIGN A SOLUTION USING AN ALGORITHM
 WRITE A COMPUTER PROGRAM
 TEST AND DEBUG THE PROGRAM
 DOCUMENT THE PROGRAM
Problem-
Solving
Phase
Implementation
Phase

3. PROBLEM SOLVING PHASE:
STEP 1: Define the problem
STEP 2: Find the solution to the problem
STEP 3: Evaluate alternative solutions
STEP 4: Represent the most efficient solution as an
algorithm
STEP 5: Test the algorithm for correctness

4. STAGE 1: DEFINING THE PROBLEM
Stating what the problem is and what the end result should
be.
A problem should be decomposed into 3 key components:
1. INPUT
2. PROCESS
3. OUTPUT

5. DEFINING THE PROBLEM
INPUT
(What is given)
OUTPUT
(The expected
output)
PROCESS
(Tasks that
must be
performed)

6. Example:
 Write a program that enters a student name and date
of birth and calculate the child’s age and write the
name and age of the child.

7. PROBLEM DEFINITION:
 Required to find the age of a child
 DEFINING DIAGRAM
INPUT PROCESS OUTPUT
1. Student Name Calculate the child’s age 1. Student Name
2. Student DOB From the child’s DOB 2. Student Age

8. Questions
1. Write a program that is required to read three (3)
numbers, calculate and print their total.
2. Give three integers representing the age of three boys
respectively, write a program to find their average and also
determine the age of the oldest boy.
3. Write a program to enter the base and height of a triangle
and find and print the area.
4. Write a program to read the temperature in degrees Celsius
and convert it to degrees Celsius and Fahrenheit.

9. PROBLEM DEFINITIONS:
1. Required to find the Total of three numbers.
2. Required to find the average age of 3 boys and the
age of the oldest boy.
3. Required to find the Area of a triangle.
4. Required to find the Fahrenheit equivalent of a
temperature in degrees Celsius.

10. DEFINING DIAGRAM: QUES. 1
INPUT PROCESS OUTPUT
NUM1 GET NUM1, NUM2,
NUM3
TOTAL/SUM
NUM2 CALCULATE TOTAL
USING NUM1,
NUM2,NUM3
NUM3 DISPLAY TOTAL

11. QUES. 2
INPUT PROCESS OUTPUT
AGE1 1. Read AGE1, AGE2,
AGE3
1.AVERAGE AGE
AGE2 2. CALCULATE
AVERAGE AGE USING
AGE1, AGE2, AGE3.
2. AGE OF OLDEST BOY
AGE 3 3. FIND AGE OF OLDEST
BOY FROM AGE1, AGE2,
AGE3
4. DISPLAY AVERAGE,
AGE OF OLDEST BOY

12. QUES. 3
INPUT PROCESS OUTPUT
BASE READ BASE, HEIGHT AREA OF TRIANGLE
HEIGHT CALCULATE AREA
USING BASE AND
HEIGHT
DISPLAY AREA

13. QUES. 4
INPUT PROCESS OUPUT
DEGREES CELCIUS READ DEGREES
CELCIUS
DEGREES FAHRENHEIT
CALCULATE DEGREES
FAHRENHEIT USING
DEGREES CELCIUS
DISPLAY DEGREES
FAHRENHEIT

14. ALGORITHMS
 An algorithm is a series of steps to be followed to
perform a task.
An algorithm should be:
1. Precise
2. Unambiguous
3. Finite (i.e. terminate after a given number of steps)
4. Instructions must be in Logical order

15. Questions
1. Identify which of the options gives the steps in correct sequence:
(a) Get on the bus, get dressed for school, get off the bus at school
(b) Get dressed for school, get off the bus at school, get on the bus
(c) Get off the bus at school, get on the bus, get dressed for school
(d) Get dressed for school, get on the bus, get off the bus at school
2. Consider the following algorithms & identify which one accurately gives the area of a square:
(a) Get length and width
Area = length x width
(b) Get side measurement of square
Area = side x side
(c) Get area of square
Area =Area x 2
(d) Get side measurement of square
Area = side x 4

16. 3. Consider the following algorithm and choose the correct
step to make it complete:
Purchase some ice-cream and toppings
Get ice-cream scoop
Use scoop to place two scoops of ice-cream on cone
Cover with sprinkles
Add a cherry to the top
(a) Eat cake
(b) Go to the cinema
(c) Purchase cone
(d) Enjoy the movie

17. VARIABLES
 A Variable is a location in memory where data of
different types are stored. When you declare a variable
the computer sets aside a location in memory to store
data.
num1 num2 sum
E.g. var num1, num2, sum: integer;

18.  A variable can be given a value or a variable can be set
to a specific value.
E.g. num1:= 1
Or the user inputs the value for num1 (1, 2, 3, 5, 90, etc.)

19.  A variable can hold ONLY one value at a time. If a new
value is entered, the old one is lost.
e.g.
5 is currently being stored in the
num1 memory location with the label,
num1 (variable). If you enter a new
value, say 15 for the variable num1,
the value 5 is replaced by the value
num1 15.
5
15

20. 1)Write a program that is required to read three (3)
numbers, calculate and print their total.
2)Write a program to enter girls’ heights. Calculate the
average height of the girls.
• Underline the variables in your program!
3)Identify all the variables in the program AreaOfSquare.

21. 1. Write an algorithm to find the sum of two numbers
and display the sum.
2. Write an algorithm to enter the name of an item, Cost
Price of an item, the number of items purchased;
calculate the Total Cost of items and display the
name of the item and total cost of the items.
3. Write an algorithm to enter a student’s name, three
marks; calculate the average mark. Display the
student’s name and average mark.

22. Program AreaOfSquare;
var s, a: integer;
Begin
write(‘Enter length of side:’);
read (s); {store length in s}
a:= s*s; {calculate area; store in a}
writeln; {print a blank line}
writeln(‘Area of square is’, a);
End.

23. VARIABLE NAMES/Identifiers
The variable name can:
• Start with a letter or underscore
• Be a combination of letters, digits and underscore
• The length of the variable name cannot exceed 31
characters
• No spaces are allowed in the variable names

24. Exercise:
 Identify the valid and invalid variable names:
R
_XYZ
Alpha;beta
Net Pay
Maxamt
Root1
2hottohandle

25. DATA TYPES
 Integer
 Real (floating point)
 String
 Boolean (data which can be true or false)
 Character (data consisting of a single character)

26. Examples of data types:
 Integer:- 3, -59, 0, 1987
 Real:- 3.142, -5.0, 1.16
 Boolean:- True or False
 Character- ‘k’, ‘8’
 String:- ‘Hi there’

27. ALGORITHMIC STRUCTURE
 Header- Algorithm’s name or title
 Declaration- A brief description of algorithm and
variables used.
 Body- sequence of steps
 Terminator- end statement

28. PSEUDOCODE
 An outline of a program, written in a form that can
easily be converted into real programming statements.

29. CONTROL STRUCTURES
 SEQUENCE
 SELECTION
 REPETITION (LOOP)

30. SEQUENTIAL STRUCTURE
 INPUT STATEMENTS. For example,
A. Get num1, num2
B. Read price
• OUTPUT STATEMENTS. For example,
A. Print Total_Cost
B. Display Average
• Statements with arithmetic operations:
A. Sum = num1 + num2
• Statements that assign values to variables:
A. Count = 0
B. Max = 20

31. SELECTION STRUCTURE
 IF-THEN-ELSE
A. If (A>B) then
Display A
B. If (age>= 50)
Print “Old”
Else
Print “Young”

32. REPETITION: LOOP
A. While (price <> 0) do
read price
total = total + price
End while
B. Repeat 10 times
Print “I am good looking”
End Repeat

33. FLOWCHARTS
 Algorithms can also be expressed as flowcharts. A
flowchart is a pictorial representation of an algorithm.
 A parallelogram- represents the input & output operation.
 A rectangle- used to represent processing/assignment
statements.
 A diamond- represents a decision (if-then-else).
 An elliptical shape- represents terminal indicators.
 Directional arrows- indicate the flow of logic in the
program.

34. INPUT/OUTPUT
PROCESSING/ASSIGNMENT
DECISION
START/STOP
FLOW OF LOGIC

35. SEQUENCE

36. DECISION

37.  FOR LOOP
REPITITION

38. WHILE LOOP

39. REPEAT UNTIL

40. http://users.evtek.fi/~jaanah/IntroC/DBeech/3gl_flow.htm

41. ARRAYS
 An array is a special variable where we reserve a series
of locations in memory to store data items of a certain
data type. These related data items are of the same
data type.

42. DECLARING AN ARRAY
 Example:
var MARKS: Array[1..35] of integer;
Reserved
word
Variable
Name
Group of
35 Data type
MARKS is the name of the entire array. In order to access one data item the
subscript is used.
MARKS
1 2 3 4 5

43. RESOURCES

44. EXERCISES