Algorithm

An algorithm is a set precise of step-by step process in how to solve a problem.

OR
An algorithm is a sequence of precise step-by-step instructions which results in a
solution.
Attributes of an algorithm:
Algorithms have four (4) very important attributes:
1. It must be precise.
2. It must be unambiguous.
3. It must be finite
4. The instructions must be in a logical sequence

Precise -The instructions or steps must be accurate since the computer cannot think
for itself.

Unambiguous -The steps must be very clear so they can be easily carried out.

Finite - The computer must have a definite number of instructions to follow and it
must come to an end.

Logical Sequence - The steps involved in the process must be related to each and
must have a clear flow from one to another.
 Structure of an Algorithm
The Header: basically stores the name/title of the Algorithm

The Declaration: a brief description of the algorithm; and the variables and
constants to be used in the algorithm
The Body: the sequence of steps including the beginning Statement
and initialization of variables
The Terminator: the ending statement

NOTE:
1. The Algorithm header must always start with the word Algorithm followed by a
colon i.e. ‘Algorithm:’.

2. The body of the algorithm must always start with the beginning statement i.e.
‘START’.

3. The Terminator must use the keyword ‘STOP’

4. In algorithm, the arrow () replaces the equal sign (=) when initializing
variables and assigning values into variables.
 Types of Algorithms

Algorithms can be represented in three (3) ways:

1. Narrative – this is where the instructions of the algorithms are written in
everyday language (English Language)

2. Pseudocode - this is where the instructions of the algorithm is written using

words and symbols that closely resemble a computer programming language
instructions.

3. Flowcharts – this is where the diagrams/shapes are used to represent the

instructions of the algorithm.

NOTE:
The following keywords are used in a Pseudocode Algorithm:
Store, set: - used in an assignment or initialization statement
If-Then-Else-Endif: - used for selection (making comparison)
While-Endwhile; Repeat-Until; For-Do: - used for iteration, repetition or loops
 Flow Chart Symbols
used to indicate the beginning/ending or start/stop of a
problem

Begin/Terminator Symbol
(Oval)
Used to indicate
processing (assignment, calculations, initialization of
variables, etc.)

Processing Symbol
(Rectangle)
Used to indicate the input and output of the problem

Input/output Symbol
(Parallelogram)
used in making a decision between two options (yes / no,
true / false)

Decision Symbol
(Rhombus)
Used to show the flow of control of steps.

Flow Control Symbol

(Arrow)
Used to connect sections of a flowchart when a flowchart is
too long and cannot fit on a page. A letter or digit can be
placed in the small circle to indicate the link on the first
Connector Symbol page. Another identically labeled connector is placed on
(Circle) the next page to indicate the continuation of flow. So, two
connectors with identical labels will serve the purpose of a
long line of flow.
 Examples of types of Algorithm

Narrative Algorithm Example 1

Problem:
Write an algorithm in narrative form to accept three numbers from the
keyboard, calculate and display their total.

Solution

Algorithm: Total_of_3_numbers Header

This algorithm will accept three numbers, calculate Declaration

and display their totals.

START Beginning statement

1. Get the three numbers. Input Statement

The Body
2. Calculate the total of the three numbers. Processing
Statement
3. Display the total of the three numbers Output
Statement

STOP Terminator Statement

Pseudocode Algorithm Example 1

Problem
Write an algorithm in pseudocode form to accept three numbers from the
keyboard, calculate and display their total.

Solution

Algorithm: Total_of_3_numbers Header

This algorithm will accept three numbers, calculate

and display their totals. The variable that will be used Declaration
are: num1, num2, num3 and total

START Beginning statement

1. Set num1 0
Set num2 0
Initialization
Set num3 0 of Variables
Set total 0 The Body

2. Get num1, num2, num3 Input Statement

3. Set total  num1+ num2 + num3 Assignment

Statement
4. Display total Output Statement

STOP Terminator Statement

Flowchart Algorithm Example 1

Problem
Draw a flowchart that will accept three numbers from the keyboard, calculate and
display their total.

Solution

Algorithm: Total_of_3_numbers Header

This algorithm will accept three numbers, calculate

and display their totals. The variable that will be Declaration
used are: num1, num2, num3 and total.

Beginning
START
statement

num10

Initialization of
num20 Variables

num30

The Body
total 0

Get num1, num2, num3 Input Statement

total  num1 + num2 + num3 Assignment

Statement
Display total Output
Statement

STOP Terminator
Statement
Narrative algorithm example 2

Problem
Write an algorithm using narrative form to accept two numbers, determine and
print the larger of the two numbers.

Solution

Algorithm: Maximum_number

This algorithm will accept two numbers, determine and print the larger of the two
numbers.

START
1. Accept two numbers

2. Check to see if the first number greater than the second number. If it is,
then;

3. output the first number

4. Otherwise, output the second number.

STOP
Pseudocode algorithm example 2

Problem
Write an algorithm using Pseudocode form to accept two numbers, determine and
print the larger of the two numbers.

Solution

Algorithm: Maximum_number

This algorithm will accept two numbers, determine and print the larger of the two
numbers. The variables that will be used are: number1 and number2.

START
1. Set number1 0
Set number2 0

2. Input number1, number2

3. If (number1 > number2) then

4. Output number1

5. Else

6. Output number2

7. Endif

STOP
Flowchart Algorithm Example 2

Problem
Draw a flowchart that will accept two numbers, determine and print the larger of
the two numbers.

Solution

Algorithm: Maximum_number

This algorithm will accept two numbers, determine and print the larger of the two
numbers. The variables that will be used are: number1 and number2.

START

Number10

Number20

Input number1, number2

number1
YES NO
>
number2

Output number1 Output number2

Endif

STOP