2. 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
3. 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.
4. 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.
5. 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”
7. 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.
8. 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
9. Flowchart Symbols
Basic
Oval
Parallelogram
Rectangle
Diamond
Hybrid
Name Symbol Use in Flowchart
Denotes the beginning or end of the program
Denotes an input operation
Denotes an output operation
Denotes a decision (or branch) to be made.
The program should continue along one of
two routes. (e.g. IF/THEN/ELSE)
Denotes a process to be carried out
e.g. addition, subtraction, division etc.
Flow line Denotes the direction of logic flow in the program
10. Example
PRINT
“PASS”
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
START
Input
M1,M2,M3,M4
GRADE(M1+M2+M3+M4)/4
IS
GRADE<50
PRINT
“FAIL”
STOP
Y
N
11. 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)
13. 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
14. Example 3
Algorithm
Step 1: Input W,L
Step 2: A L x W
Step 3: Print A
START
Input
W, L
A L x W
Print
A
STOP
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2005 15
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.
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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.
17. Principles of Programming - NI July
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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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Flowchart – sequence control structure
Statement 2
Statement 1
Statement 3
:
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Flowchart – selection control structure
Condition
else-
statement(s)
then-
statement(s)
Yes
No
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Flowchart – repetition control structure
Condition
Loop
Statement(s)
yes
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
End
Age > 55? NO
YES
print “Pencen” print “Kerja lagi”
23. Principles of Programming - NI July
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Flowchart – example 5
Begin
End
current_number <= 10?
NO
YES
sum = 0
current_number = 1
sum = sum + current_number
current_number = current_number + 1
print sum
24. Example 4
Write an algorithm and draw a flowchart that
will calculate the roots of a quadratic equation
Hint: d = sqrt ( ), and the roots are:
x1 = (–b + d)/2a and x2 = (–b – d)/2a
2
0
ax bx c
2
4
b ac
27. 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.
28. Lab Activity: Algorithm &
Flowchart
4) Create an algorithm and a flowchart that
will output the largest number among the
three numbers.
29. 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.
