1. PROGRAMMING PAPER 2 AS
Algorithms

2. What it’s all about
Problem Solving
Algorithm
Pseudo codes
Flowcharts

3. At the end of this you should be able to :
Understand Problem definitions
Solve these using Algorithms
Solve these using Flowcharts
Be able to identify, define and understand various programming terms

4. Key Terms You should know what these terms are and when to use them
program
pseudocode
flowchart
algorithm

5. Problem Solving Techniques
Here you will learn about:
What problem solving is
The software development method of problem solving using computers
Basic algorithm control structures
The sequence structure
The selection structure
The repetition structure

6. Problem Solving Techniques
What do they translate to :
Apply the software development method to solve problems
Difference between the Algorithm & the Flowchart
Knowing about the control structures

7. What do you do first First : Read the question and understand it
UNDERSTAND THE PROBLEM
What is the objective?
What are the data?
What is the condition?
Is it possible to satisfy the condition?
Is the condition sufficient to determine the unknown?

8. Problem Solving Second: DEVISING A PLAN
Find the connection between the data and the unknown.
Auxiliary problems may be devised if needed.
DEVISING A PLAN
Have you seen it before?
Or have you seen the same problem in slightly different form?
Do you know a related problem?
Split the problem into smaller, simple sub-problems.
If you cannot solve the proposed problem try to solve first some related problem. Or solve more general problem. Or special case of the problem. Or solve the part of the problem.

9. Problem Solving CARRYING OUT THE PLAN WHAT DID YOU DO, THINK BACK
Third:
Carry out your plan.
CARRYING OUT THE PLAN
Carrying out your plan of the solution, check each step.
Fourth:
Examine the solution obtained.
WHAT DID YOU DO, THINK BACK
Can you derive the result differently? Can you use the result, or the method, for some other problem?

10. The software development method
Slightly off track…
The software development method
The software development method consists of the following steps:
Requirements specification
Analysis
Design
Implementation
Testing and verification
Documentation

11. Algorithmic Problem Solving
Algorithmic problem: Any problem whose solution can be expressed as a set of executable instructions. Algorithm: A well defined computational procedure consisting of a set of instructions, that takes some value or set of values, as input, and produces some value or set of values, as output.

12. Characteristics of an Algorithm
Each step of an algorithm must be exact, preciously and unambiguously described.
It must terminate, i.e. it contains a finite number of steps.
It must be effective, i.e.., produce the correct output.
It must be general, i.e.. to solve every instance of the problem.

13. Characteristics of an Algorithm
An Algorithm is implemented in some programming language.
program = Algorithm + Data Structures.
Data Structures refer to the types of data used and how the data are organized in the program.
An algorithm is usually presented in the form of some pseudo-code, which is a mixture of English statement,some mathematical notations,and selected keywords from a programming language.

14. Characteristics of an Algorithm
An Algorithm should emphasize the WHAT’s and not the HOW’s. Consider the problem below:
PROBLEM:
You are required to design a complete system which will enable the sum of two values to be calculated.

15. Problem Solving
To grapple with this problem, we have to understand the problem from the human perspective.
A question to ask yourself is this,
“How Would You Calculate the Sum of Two Values?”

16. What Are Variables?
Variables are memory locations within the computer which allows pieces of data to be stored.
The word variable comes from the word vary, which means that whatever you place within a variable can be changed.
A variable can be viewed as a container used to store things.
Data (for example, name, age, salary) can be stored in these containers.

17. Defining diagram Input Processing Output
Now that we have an exact idea about how the problem is solved, let us represent this in a clearer manner, using the defining diagram.
Input
Processing
Output
Value1
Value2
Sum

18. LIST THE STEPS
The next step is to identify the actual processing steps required to convert the input to become the output.
Input
Processing
Output
Value1
Value2
1) Read Value1, Value2
2) Calculate Sum
3) Display Sum
Sum

19. Algorithm Development
Once the defining diagram has been developed, the next logical step is to develop the algorithm (which is much more detailed).
Input
Processing
Output
Value1
Value2
1) Read Value1, Value2
2) Calculate Sum
3) Display Sum
Sum
The developed processing steps have to be more detailed in the algorithm.

20. Algorithm Development
The basic mathematical operators used in algorithms are as follows:-
+ addition
- subtraction
* multiplication
/ division
= assignment
( ) brackets for grouping calculations

21. Algorithm Development
Example of an algorithm (using pseudocodes) which can be used to carry out the tasks outlined in the defining diagram is as follows:-
1) Read Value1, Value2
2) Calculate
Sum = Value1 + Value2
3) Display Sum

22. Pseudocoding
A Pseudocode language is semiformal, English-like language with a limited vocabulary that can be used to design and describe algorithms.
The pseudocode language can be used for:
Designing algorithms
Communicating algorithms as programs
Implementing algorithms as programs
Debugging logic errors in program

23. Pseudocode for the Control Structures
The Sequence Control Structure:
The sequence control structure is a series of steps or statements that are executed in the order in which they are written in an algorithm.
For Example:
read taxable income
read filing status
compute income tax

24. Cont’d The Selection Control Structure:
The Selection Control Structure:
The selection control structure defines two courses of action, depending on the outcome of a condition. A condition is an expression that, when evaluated, computes to either true or false.
Syntax is: if condition
then-part
else
else-part
end-if

25. Decision Making
Being able to mimic the way the human brain works, the computer also has the ability to make decisions.
Decision making can be represented in pseudocodes using the IF...THEN construct.
IF (expression) THEN :
ENDIF

26. Decision Making
The expression is a comparison between two values which evaluates to either true of false.
IF (expression) THEN :
ENDIF
Statements are placed here.

27. Decision Making Example:-
We are looking for a job which pays more than Rs
Example of an Expression
IF (Salary>4000) THEN
Say "I Will Take The Job!!"
ENDIF

28. Decision Making Commonly used relational operators in expressions:-
> Greater Than
< Less Than
= Equals To
< > Not Equals To
>= Greater Than or Equals To
<= Less Than or Equals To
( ) Brackets used for prioritising certain calculations

29. Decision Making
Since all expressions works out to be either true or false, what the IF..THEN statement represents is a two-state condition.
For example,
A potential employer is waiting for you to give a reply (on the spot) about the job offer with a salary of Rs Your decision would be to only take a job worth more than RM4000. What would you say?
IF (Salary>4000) THEN
Say “YES!”
ELSE
Say “NO!”
ENDIF

30. Decision Making
Certain conditions may give rise to more than one expression being evaluated. These are known as compound expressions.
Example:-
You are interested in taking up a job which pays more than Rs.4000 and that the company must also provide a credit card.
IF (Salary>4000) And (CreditCard=YES) THEN
Take Job!!
ENDIF

31. Decision Making
Compound expressions can be represented using the following operators:-
AND Every expression must evaluate to be true in order for the whole expression to be true.
OR As long as any one of the expression can be true, the entire IF statement will be true.
NOT The inverse (opposite) of the entire expression.

32. Decision Making
IF statements can be nested, that is, placed within another IF statement.
This is used in situations when the expression is more complex than the simple decisions (as seen earlier).

33. Decision Making For example, this statement.........
IF (Salary>4000) And (CreditCard=YES) THEN
Say “Yes I Will Take The Job!!”
ENDIF
can be represented like this
IF (Salary>4000) THEN
IF (CreditCard=YES) THEN
Say “Yes I Will Take The Job!!”
ELSE
Say “No Credit Card?”
Say “Sorry!!”
ENDIF
Say “Not Enough Pay!!”
whereby more possibilities can be represented.

34. Decision Making For good practice...........
IF (Salary>4000) THEN
IF (CreditCard=YES) THEN
Say “Yes I Will Take The Job!!”
ELSE
Say “No Credit Card?”
Say “Sorry!!”
ENDIF
Say “Not Enough Pay!!”
ensure that statements are properly indented to indicate block of statements which belong together.

35. Cont’d For Example: if a is greater than b then print “A is greater”
For Example:
if a is greater than b then
print “A is greater”
else
print “B is greater”
end if

36. Cont’d Repetition Control Structure:
Repetition Control Structure:
The repetition control structure specifies a block of one or more statements that are repeatedly executed until a condition is satisfied.
Syntax is:
while condition
loop-body
end-while

37. ITERATIVE STATEMENTS
Looping constructs (also known as repetition or iteration constructs) are a kind of construct found in pseudocodes which allows statements (or a group of statements) to be repeated.
The main reason why looping constructs are provided is because most of the problems which we encounter everyday requires some degree of repetition.

38. ITERATION EXAMPLE An example of a process which is iterative:-
Processing Pay of teachers by the school is very much an iterative process as the person processing the payroll applies the same calculations for each employee to produce the pay slip.

39. TYPES OF LOOPS
The looping constructs available in pseudocodes are as follows:-
DOWHILE...ENDDO
FOR…NEXT
REPEAT...UNTIL

40. DO WHILE LOOP
The format of the DOWHILE...ENDDO construct is shown below:-
DOWHILE (expression) :
ENDDO
Group of statements
An expression which determines whether the loop will continue.

41. FOR LOOP The format of the FOR...NEXT construct is shown below:-
FOR (initialze TO expression) STEP increment :
ENDDO
Group of statements
An expression which determines whether the loop will continue.

42. REPEAT…UNTIL
The format of the REPEAT...UNTIL construct is shown below:-
REPEAT :
UNTIL (expression)
Group of statements
An expression which determines whether the loop will continue.

43. Looping Constructs Take a look at the following example:-
You are required to develop a complete system which will allow the total payroll to be calculated.
The system is required to read in the amount to be paid for each employee.
The moment the system receives an input value of -99, the system is required to stop and display the total payroll.

44. Looping Constructs The Defining Diagram Input Processing Output Salary
1) Read Salary
2) Calculate Total
3) Display Total
Total

45. Looping Constructs Algorithm (Using Pseudocodes)
1) Display "Enter Salary"
2) Read Salary
3) Total = 0
4) DOWHILE (Salary<>-99)
Total = Total + Salary
Display "Enter Salary"
Read Salary
ENDDO
5) Display "Total Payroll = ", Total

46. Cont’d Example: Dowhile (income is less than 50000)
Example:
Dowhile (income is less than 50000)
print “Enter taxable income;should be
greater than or equal to 50000”
read income
Enddo

47. Program Flowcharts
As humans are more inclined towards understanding diagrams and pictures rather than words, pseudocodes tends to become tedious to understand if too lengthy.
Program flowcharts, because they are represented graphically, makes understanding easier.

48. Program Flowcharts
The following are the commonly used symbols for drawing program flowcharts.
off-page connector
terminator
process
storage
decision
making
document
input/output
connector
arrowheads

49. Program Flowcharts Begin Read Value1, Value2 Calculate
Sum = Value1 + Value2
Display
Sum
End

50. Program Flowcharts Begin Read Amount YES NO Amount>20.00? Calculate
Actual=Amount * 0.80
Calculate
Actual=Amount
End

51. Flowcharting
Another technique used in designing and representing algorithms.
Alternative to pseudocoing
A pseudocode description is verbal, a flowchart is graphical in nature.
Definition:
A flowchart is a graph consisting of geometrical shapes that are connected by flow lines.

52. Sequence Structure Statement -1 Statement -2 Statement -n
Pseudocode: Flowchart:
statement_1
statement_2
statement_n
Statement -1
Statement -2
Statement -n

53. Selection Structure false condition true else-part then-part
Pseudocode: Flowchart:
if condition
then-part
else
else-part
end_if
false
condition
true
else-part
then-part

54. Selection Structure true condition then-part false
Pseudocode: Flowchart:
if condition
then-part
end_if Y
condition
true N
then-part
false

55. Repetition Structure condition loop-body Pseudocode: Flowchart:
while condition
loop-body
end-while T
condition Y
loop-body F N

56. Summary
Problem Solving– the process of transforming the description of a problem to its solution.
To Solve complex problems, we use computers as a tool and develop computer programs that give us solutions.
A commonly used method for problem solving using computers is the software development method,which consists of six steps.

57. Summary
An algorithm is a sequence of a finite number of steps arranged in a specific logical order that, when executed, produce the solution for a problem.
A pseudocode language is a semiformal,English-like language with a limited vocabulary that can be used to design and describe algorithms.

58. Summary
Any algorithm can be described in terms of three basic control structures.They are the sequence,selection and repetition structures.
The top-down stepwise refinement of algorithms is a fundamental problem-solving strategy.
A Flowchart is a graphical representation of an algorithm.

59. Quick Review Question
State the difference between the Dowhile – Enddo structure and the
Repeat – Until structure.
Write an algorithm that will display the first hundred even numbers
using the Do-While loop.