Algorithms and flowcharts

ALGORITHMS &
FLOWCHARTS
Monday, November 21, 2016

LEARNING OUTCOMES
At the end of the lesson, I should be able to:
a. -Define algorithm, Pseudo codes and flowchart
b. -State characteristics of Algorithms
c. -Outline functions of Algorithm
d. -Write algorithm for solving a given problem
e. -Flowchart symbols and their uses
f. -Translating algorithms to flowchart programs
g. -Draw flowcharts for solving given problems

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
1. First produce a general algorithm: (one can
use pseudo code)
2. Refine the algorithm successively to get
step by step detailed algorithm that is very
close to a computer language.
3. Pseudo code is an artificial and informal
language that helps programmers develop
algorithms. Pseudo code is very similar to
everyday English.

PSEUDOCODE & ALGORITHM
1. 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.

Pseudo code:
1. Input a set of 4 marks
2. Calculate their average by summing and
dividing by 4
3. 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
A Flowchart is a graphical representation of the sequence
of operations in an information system or program.
Flowchart Characteristics:
1. shows the sequence of instructions in a single program or
subroutine
2. shows logic of an algorithm from start to finish
3. emphasizes individual steps and their interconnections
4. control flow from one action to the next
5. Different symbols are used to draw each type of flowchart
6. The start symbol indicates the beginning of a program
7. The end symbol indicate the end of a program.

FLOWCHART SYMBOLS
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
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

FLOWCHART SOLUTION TO EXAMPLE 1
PRINT
“PASS”
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
START
Input
M1,M2,M3,M4
GRADE(M1+M2+M3+M4)/4
IS
GRADE<5
0
PRINT
“FAIL”
STOP
YN

EXAMPLE 2
Write an algorithm and draw a flowchart to convert
the length in feet to centimeter.
Pseudo code:
1. Input the length in feet (Lft)
2. Calculate the length in cm (Lcm) by multiplying
LFT with 30
3. Print length in cm (LCM)

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
1. Input the width (W) and Length (L) of a
rectangle
2. Calculate the area (A) by multiplying L with
W
3. Print A

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

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
0ax bx c  
2
4b ac

Pseudo code:
1. Input the coefficients (a, b, c) of the quadratic
equation
2. Calculate d
3. Calculate x1
4. Calculate x2
5. Print x1 and x2

Algorithm:
Step 1: Input a, b, c
Step 2: d  sqrt ( )
Step 3: x1  (–b + d) / (2 x a)
Step 4: x2  (–b – d) / (2 x a)
Step 5: Print x1, x2
4b b a c   
START
Input
a, b, c
d  sqrt(b x b – 4 x a x c)
Print
x1 ,x2
STOP
x1 (–b + d) / (2 x a)
X2  (–b – d) / (2 x a)

ASSIGNMENT
Provide the answer to question number 4 on page
109 of your HiiT textbook.

TERMINOLOGIES
An algorithm is a step by step procedure in solving a
problem
Pseudo code is an artificial and informal language
that helps programmers develop algorithms. Pseudo
code is very similar to everyday English.
Flowchart is a graphical representation of the
sequence of operations in an information system or
program.

ALGORITHMS &
FLOWCHARTS II
Monday, November 21, 2016

DECISION STRUCTURES
 The expression A>B is a logical expression
 it describes a condition we want to test
 if A>B is true (if A is greater than B) we take
the action on left
 print the value of A
 if A>B is false (if A is not greater than B) we
take the action on right
 print the value of B

DECISION STRUCTURES
is
A>B
Print
B
Print
A
Y N

IF–THEN–ELSE STRUCTURE
 The structure is as follows:
If condition then
true alternative
else
false alternative
endif

IF–THEN–ELSE STRUCTURE
 The algorithm for the flowchart is as follows:
If A>B then
print A
else
print B
endif
is
A>B
Print
B
Print
A
Y N

RELATIONAL OPERATORS
Relational Operators
Operator Description
> Greater than
< Less than
= Equal to
 Greater than or equal to
 Less than or equal to
 Not equal to

EXAMPLE 5
 Write an algorithm that reads two values,
determines the largest value and prints the largest
value with an identifying message.
ALGORITHM
Step 1: Input VALUE1, VALUE2
Step 2: if (VALUE1 > VALUE2) then
MAX  VALUE1
else
MAX  VALUE2
endif
Step 3: Print “The largest value is”, MAX

MAX  VALUE1
Print
“The largest value is”,
MAX
STOP
Y N
START
Input
VALUE1,VALUE2
MAX  VALUE2
is
VALUE1>VALUE2

NESTED IFS
 One of the alternatives within an IF–THEN–ELSE
statement
 may involve further IF–THEN–ELSE statement

EXAMPLE 6
 Write an algorithm that reads three numbers and
prints the value of the largest number.

Step 1: Input N1, N2, N3
Step 2: if (N1>N2) then
if (N1>N3) then
MAX  N1 [N1>N2, N1>N3]
else
MAX  N3 [N3>N1>N2]
endif
else
if (N2>N3) then
MAX  N2 [N2>N1, N2>N3]
else
MAX  N3 [N3>N2>N1]
endif
endif
Step 3: Print “The largest number is”, MAX

EXAMPLE 7
 Write and algorithm and draw a flowchart to
a) read an employee name (NAME), overtime hours
worked (OVERTIME), hours absent (ABSENT)
and
b) determine the bonus payment (PAYMENT).

Step 1: Input NAME,OVERTIME,ABSENT
Step 2: if (OVERTIME–(2/3)*ABSENT > 40) then
PAYMENT  50
else if (OVERTIME–(2/3)*ABSENT > 30) then
PAYMENT  40
PAYMENT  30
PAYMENT 20
else
PAYMENT  10
endif
Step 3: Print “Bonus for”, NAME “is $”, PAYMENT

Bonus Schedule
OVERTIME – (2/3)*ABSENT Bonus Paid
>40 hours
>30 but  40 hours
 10 hours
$50
$40
$30
$20
$10

Algorithms and flowcharts

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