ALGORITHMS AND
FLOWCHARTS
ALGORITHMS AND FLOWCHARTS
A typical programming task can be divided into
two phases:
Problem solving phase
produce an ordered sequence of steps that describe
solution of problem
this sequence of steps is called an algorithm
Implementation phase
implement the program in some programming
language
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Steps in Problem Solving
First produce a general algorithm (one can use
pseudocode)
Refine the algorithm successively to get step by
step detailed algorithm that is very close to a
computer language.
Pseudocode is an artificial and informal
language that helps programmers develop
algorithms. Pseudocode is very similar to
everyday English.
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Pseudocode & Algorithm
Example 1: Write an algorithm to
determine a student’s final grade and
indicate whether it is passing or failing.
The final grade is calculated as the
average of four marks.
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Pseudocode & Algorithm
Pseudocode:
Input a set of 4 marks
Calculate their average by summing and dividing
by 4
if average is below 50
Print “FAIL”
else
Print “PASS”
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Pseudocode & Algorithm
Detailed Algorithm
Step 1: Input M1,M2,M3,M4
Step 2: GRADE (M1+M2+M3+M4)/4
Step 3: if (GRADE < 50) then
Print “FAIL”
else
Print “PASS”
endif
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The Flowchart
(Dictionary) A schematic representation of a sequence of
operations, as in a manufacturing process or computer
program.
(Technical) A graphical representation of the sequence of
operations in an information system or program.
Information system flowcharts show how data flows from source
documents through the computer to final distribution to users.
Program flowcharts show the sequence of instructions in a single
program or subroutine. Different symbols are used to draw each
type of flowchart.
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The Flowchart
A Flowchart
shows logic of an algorithm
emphasizes individual steps and their
interconnections
e.g. control flow from one action to the next
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Flowchart Symbols
Terminal symbol - indicates the beginning and
end points of an algorithm.
Process symbol - shows an instruction other than
input, output or selection.
Input-output symbol - shows an input or an output
operation.
Disk storage I/O symbol - indicates input from or output to
disk storage.
Printer output symbol - shows hardcopy printer
output.
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Flowchart Symbols cont…
Selection symbol - shows a selection process
for two-way selection.
Off-page connector - provides continuation of a
logical path on another page.
On-page connector - provides continuation
of logical path at another point in the same
page.
Flow lines - indicate the logical sequence of
execution steps in the algorithm.
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Example 1
Pseudocode:
Input a set of 4 marks
Calculate their average by summing and dividing
by 4
if average is below 50
Print “FAIL”
else
Print “PASS”
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Example 1
START
Algorithm
Step 1: Input M1,M2,M3,M4
Input
M1,M2,M3,M4
Step 2: GRADE (M1+M2+M3+M4)/4
Step 3: if (GRADE <50) then
Print “FAIL”
GRADE(M1+M2+M3+M4)/4 else
Print “PASS”
N
endif
IS Y
GRADE<5
0
PRINT PRINT
“PASS” “FAIL”
STOP
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Example 2
Write an algorithm and draw a flowchart to
convert the length in feet to centimeter.
Pseudocode:
Input the length in feet (Lft)
Calculate the length in cm (Lcm) by
multiplying LFT with 30
Print length in cm (LCM)
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Example 2
Flowchart
Algorithm START
Step 1: Input Lft
Input
Step 2: Lcm Lft x 30
Lft
Step 3: Print Lcm Lcm Lft x 30
Print
Lcm
STOP
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Example 3
Write an algorithm and draw a flowchart that
will read the two sides of a rectangle and
calculate its area.
Pseudocode
Input the width (W) and Length (L) of a rectangle
Calculate the area (A) by multiplying L with W
Print A
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Example 3
Algorithm START
Step 1: Input W,L Input
W, L
Step 2: A L x W
Step 3: Print A ALxW
Print
A
STOP
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Flowcharts
Flowcharts is a graph used to depict or
show a step by step solution using
symbols which represent a task.
The symbols used consist of geometrical
shapes that are connected by flow lines.
It is an alternative to pseudocoding;
whereas a pseudocode description is
verbal, a flowchart is graphical in nature. 17
Flowchart – sequence control structure
Statement 1
Statement 2
Statement 3
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Flowchart – selection control structure
No Yes
Condition
else- then-
statement(s) statement(s)
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Flowchart – repetition control structure
yes Loop
Condition
Statement(s)
no
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Flowchart – example 1
Begin
Read birth date
Calculate
Age = current year – birth date
Display
age
End
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Flowchart – example 2
Begin
Read age
YES Age > 55? NO
print “Pencen” print “Kerja lagi”
End
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Flowchart – example 5
Begin
sum = 0
current_number = 1
NO
current_number <= 10? print sum
YES
End
sum = sum + current_number
current_number = current_number + 1
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Exercises: Algorithm &
Flowchart
1.) Create an algorithm and a flowchart that
will accept/read two numbers and then
display the bigger number.
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Exercises: Algorithm &
Flowchart
2.) Create an algorithm and a flowchart that
will compute the area of a circle.
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Exercises: Algorithm &
Flowchart
3.) Create an algorithm and a flowchart that
will compute the sum of two numbers. If
the sum is below or equal to twenty, two
numbers will be entered again. If the sum
is above 20, it will display the sum.
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Lab Activity: Algorithm &
Flowchart
4) Create an algorithm and a flowchart that
will output the largest number among the
three numbers.
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Assignment 1
1. Create an algorithm and a flowchart that will output for g.c.d.
2. Create an algorithm and a flowchart that will output the factorial of a
given number.
3. Create an algorithm and a flowchart that will output the Fibonacci
series up to a given number.
4. Create an algorithm and a flowchart that will output all the prime
numbers between 2 numbers.
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