Lect1-Algorithms-and-Flowchart PPT presentation

ALGORITHMS AND
FLOWCHARTS
Lecture 1: Problem Analysis
By: Ashutosh Mishra

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

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.

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.

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”

 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

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.

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

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

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

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)

Example 2
Algorithm
 Step 1: Input Lft
 Step 2: Lcm  Lft x 30
 Step 3: Print Lcm
START
Input
Lft
Lcm  Lft x 30
Print
Lcm
STOP
Flowchart

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

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

Principles of Programming - NI July
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.

2005 16
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.

2005 17
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.

2005 18
Flowchart – sequence control structure
Statement 2
Statement 1
Statement 3
:

2005 19
Flowchart – selection control structure
Condition
else-
statement(s)
then-
statement(s)
Yes
No

2005 20
Flowchart – repetition control structure
Condition
Loop
Statement(s)
yes
no

2005 21
Flowchart – example 1
Begin
Read birth date
Calculate
Age = current year – birth date
Display
age
End

2005 22
Begin
Read age
End
Age > 55? NO
YES
print “Pencen” print “Kerja lagi”

2005 23
Begin
End
current_number <= 10?
NO
YES
sum = 0
current_number = 1
sum = sum + current_number
current_number = current_number + 1
print sum

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


Exercises: Algorithm &
Flowchart
1.) Create an algorithm and a flowchart that
will accept/read two numbers and then
display the bigger number.

Flowchart
will compute the area of a circle.

Flowchart
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.

Lab Activity: Algorithm &
Flowchart
4) Create an algorithm and a flowchart that
will output the largest number among the
three numbers.

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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