1. ALGORITHM Basic CONCEPTS of Basic Concepts of Algorithm
Siti Nurbaya Ismail
Senior Lecturer
Faculty of Computer & Mathematical Sciences
Universiti Teknologi MARA Kedah (e): (u):

2. Previously…
A program MUST be systematically and properly designed before coding begins. This design process results in the construction of an ALGORITHM.

3. Algorithm design At the end of this chapter you will be able to;
List the characteristics of an algorithm
List the algorithm presentation
Differentiate between pseudocode and flowchart
Understand how computer executes an algorithm
Know how to trace an algorithm
Construct basic algorithm using pseudocode and flowchart to solve problems

4. Algorithm
Is a sequence of steps that tells how to solve a particular problem. An algorithm must be:
Step-by-step method for solving a problem
Must be a well defined and well ordered sequence of instruction.
All instruction must be able to perform
Must produce a result
Must have a finite number of steps
Most agree that algorithm has something to do with defining generalized processes to get “output” from the “input”.

5. Algorithm & Logical Thinking
To develop the algorithm, the programmer needs to ask:
What data has to be fed into the computer?
What information do I want to get out of the computer?
Logic: Planning the processing of the program. It contains the instructions that cause the input data to be turned into the desired output data.

6. Algorithm Therefore, we can conclude that:
Algorithm a step‐by‐step problem solving process in which a solution is arrived in a finite amount of time OR
An algorithm is a finite list of sequential steps specifying actions that if performed result in solution of a specific problem.

7. From Algorithm to Program
a set of instructions which are commands to computers to perform specific operations on data
a sequence of instructions describing how to do a task (or process)

8. History of algorithm
The word algorithm comes from the name of the 9th century Persian Muslim mathematician Abu Abdullah Muhammad ibn Musa Al- Khwarizmi.
The word algorism originally referred only to the rules of performing arithmetic using Hindu-Arabic numerals but evolved via European Latin translation of Al-Khwarizmi's name into algorithm by the 18th century.
The use of the word evolved to include all definite procedures for solving problems or performing tasks.

9. Algorithm Representation
Two types of representation:
Graphically – flowchart
Textual – pseudocode
Flowchart
Graphical or symbolic representation to present steps in algorithm.
Each symbol has a specific meaning containing a short description of a step.
The flowchart symbols are linked together with arrows showing flow direction
Pseudo code
consist of short English phrases used to describe steps in algorithm.
Start with start or begin and ends with stop or end

10. Flowchart Symbol and Description
Name
Symbol
Description
Lozenge
Indicates the starting or ending of flowchart (start / stop : terminal )
Connector
Used to connect break in the flowchart
Parallelelogram
Use for input and output operation (data)
Rectangle
Indicates any interval operation (process)
Diamond
Use for asking questions that can have either TRUE of FALSE / YES or NO (decision / selection)
Module
Sub solution to solve a part of entire problem
Control flow
Shows flow direction

11. Flowchart Logic Structure
Sequence Structure
Selection Structure
Loop Structure
DO WHILE
(test condition)
LOOP
(statement) No
Yes
ELSE
(statement) IF
(test condition)
THEN No
Yes
statement

12. Sequence Structure
With sequence structure, an action or event is performed in order, one after another.
A sequence can contain any number of events but there is no chance to branch off and skip any of the events.
Once you start a series of events in a sequence, you must continue step‐by‐step until the sequence ends.

13. Sequence Structure – Example 1
To find the area of a rectangle
The formulas: area = length * width
Flowchart Example
Start
length, width
area = length x width
area
End
Problem definition
Data
Formula
Information
Input variable:
length
width
area = length x width
Output:
area
Algorithm
Step / Solution:
1. get input
2. calculate area, area = length x width
3. display area

14. Pseudo Code Example OR OR To find the area of a rectangle
The formulas: area = length * width
Pseudo Code Example
Problem definition
Data
Formula
Information
Input variable:
length
width
area = length x width
Output:
area
Start Read length Read width area = length x width Display area of a rectangle End
Algorithm
Start
Input length
Input width
Calculate area of a rectangle
Output area of a rectangle
End
Step / Solution:
1. get input
2. calculate area, area = length x width
3. display area of rectangle OR
Start
Prompt the user to enter a length of a rectangle
Prompt the user to enter a width of a rectangle
Calculate the area of a rectangle
Display the area of a rectangle
End OR

15. Sequence Structure - Example 2
Problem
Design a software to calculate the sum of two numbers entered by user.
Data
Formula
Information
Input variable:
num1
num2
sum = num1 + num2
Output:
sum
Algorithm
Step / Solution algorithm:
1. get num1, num2
2. calculate sum = num1 + num2
3. display sum

16. Sequence Example Pseudo Code Simple Design Modular Design
Start
Read num1
Read num2
Calculate sum
sum = num1 + num2
Print sum
End
Modular Design
Start
get_input()
calculate_sum()
display_output()
End
Module get_input()
Read num1
Read num2
Return
Module calculate_sum()
sum = num1 + num2
Module display_output()
Print sum

17. Sequence Example Flowchart Simple Design Modular Design Sub-Module
Start
start
Read num1, num2
sum = num1 + num2
Print sum
end
Start
Read num1
Read num2
Return
get_input()
Start
calculate_sum()
calculate sum
display_output()
Return
Start
End
Print sum
Return

18. Why Algorithm is Important?
Describe the steps needed to perform a computation
Important for writing efficient code
code that execute faster & which uses less memory

19. Tracing an algorithm
The purpose to trace an algorithm is to understand how computer executes the given algorithm.
We also can see what will happen in the computer memory and what is the result or information of the algorithm.
Step to trace a given algorithm:
list all the variables in the algorithm
create locations for each of them
execute each statement and at the same time change the value of variables involved.

20. Tracing an algorithm Example 1
Start 1. Display “Enter a length : “ 2. Read length 3. Display “Enter a width : “ 4. Read width 5. area  length x width 6. Display “The area of a rectangle : “ , area End
Assume that the user enters 7 and 5. What will happen when we trace the above algorithm ?

21. Tracing an algorithm Example 1 length width area 7 5 7*5=35
Start 1. Display “Enter a length : “ 2. Read length 3. Display “Enter a width : “ 4. Read width 5. area  length x width 6. Display “The area of a rectangle : “ , area End
Assume that the user enters 7 and 5. What will happen when we trace the above algorithm ?
The following diagram shows activities in the computer memory:
length
width
area 7 5
7*5=35

22. Tracing an algorithm Example 2 Start
Display “Enter marks for 3 tests :”
Read test1, test2, test3
Display ” Enter marks for 4 quizzes :”
Read qz1, qz2, qz3, qz4
Display ” Enter final exam mark :”
Read final-exam
test-mark  ( test1 + test2 + test3)/3
quiz-mark ( qz1 + qz2 + qz3 + qz4 )/4
carry-mark  20% x test-mark + 20% x quiz-mark
final-mark  carry-mark + 60% x final-exam
Display message “Final mark : “, final-mark
End
Assume that the user enters What will happen when we trace the above algorithm ?

23. Tracing an algorithm Example 2
Assume that the user enters What will happen when we trace the above algorithm ? The following diagram shows what will happen in the computer memory.
test1
test2
test3
quiz1
quiz2
quiz3
quiz4
finalExam
testMark
quizMark
carryMark
finalMark 60 90 80 70 /3
=80 /4
=72.5
0.2*80 +
0.2*72.5
=30.5
30.5+
0.6*90
=84.5

24. Write A Basic Algorithm Using Pseudocode
Using words to explain the steps to solve problem
Start  Start
Content  activities/statements/instructions
 normally the arrangement of activities/statements/instructions
 start with input data
 follow by data manipulation(processing statements)
 ends with output/print/display the result/information
End  End

25. Guidelines In Designing Algorithm in Pseudocode
Firstly, write a basic algorithm before proceeding with the detailed algorithm.  get idea on how to solve the problem
read, input, prompt, get  to accept input from user
calculate, compute, =  data manipulation (perform processing)
display, output, print, write  to convey information

26. EXERCISES

27. Exercise 1 Based on the following picture, answer the given question.
Write a pseudocode to calculate the shaded area in the following area.
Assume that the user enters value as in the picture. What will happen when we trace the above algorithm ? 35 17 23 8

28. shaded_area = total_area – bright_area
Pseudocode Start Read Length(t) Read Width(t) Read Length(b) Read Width(b) Calculate total_area = Width(t)*Length(t) Calculate bright_area = Width(b)*Length(b) Calculate shaded_area = total_area-brigth_area Display shaded_area End
Start
Read lt, wt,lb,wb
Calculate
total_area = lt*wt
bright_area = lb*wb
shaded_area = total_area – bright_area
Display shaded_area
End

29. Exercise 2
Ask the user to enter a time in unit second. Convert the value into hour, minute and second. Write a pseudocode and trace the algorithm, assume user enter 3740

30. Exercise
For each of the problem, analyze it using IPO table, then write the algorithm (pseudo code and flowchart).
Problem 1: Calculate the area of one circle.
Problem 2: Calculate the temperature in Celsius. Temperature in Fahrenheit will be entered. The formula is;
Temperature in Celsius = 5/9 (temperature in Fahrenheit – 32)
Problem 3: Calculate the final mark for a student who took CS118 paper. The final mark is the total of on-going assessment (carry mark) and 60% of final exam. The carry mark is calculated as follow:
Carry mark = 20% of test mark + 20% of quiz mark

31. EXERCISE
Chapter 3: Exercise 3B all