Naming, Algorithms#1 CTPS 2018 · 2019. 5. 20. · 1. Start 2. Declare sum, count, num 3. Set sum = 0, count = 0 (Initialize) 4. Enter num (Input /Read ) 5. Find sum + num and assign

Department of CSE,Coimbatore

Naming, Algorithms#1

CTPS 2018

LN #4

(2 Hrs)

Objectives

❖To understands the importance of naming

❖To understand the characteristics of algorithms

❖To learn to write algorithms


Names

• An identifier (or name) is used to identify the entities, eg., variables,

module names.

• Naming conventions increase readability.

Good naming practices

1. Never use I (lowercase L ) or O (uppercase O ) as variable or constant

names.(Confused for 1 or a 0)

2. What about the length of the name?

“total_number_of_entries_with_mangled_or_out_of_range_dates ”?

• This is an extremely descriptive name.

• First, they are difficult to type.

• Second, remembering the exact wording of such a long name is not easy.

• What happens when you try to use this variable in a statement?Department of CSE,Coimbatore

3. Connection character (e.g. first_name, First-name)

• What about first$name???

4. Case sensitivity (e.g.Name,name,NAME)

5. Don´t use negative logic for your variable names.

• Good Example: IsEnabled.

• Bad Example: IsNotEnabled.

It’s always easier to read and understand a statement that is expressed in a positive language than that in a negative language.

7. Reserved words or keywords?

• (PI, Cu(copper))

• What about assigning PI=24(hours of a day), Cu in chemistry to represent metal gold?


Guidelines for Naming

• Names should be unique.

• One item should not have more than one name.

• Eg. “get the data”,using multiple words like “load”, “fetch”, “get” may be

confusing.

• A name should be descriptive. Eg. FileAgeInDays is better than

“faid”.

• Descriptive names reduce confusion.

• They help us understand the role of the item.

• They help us to understand the content of the item.


Try it yourself

✓Assume that a user need to create an e-mail account. List the fields

required to be filled in registration form and suggest suitable names,

datatype (number, string, boolean) and range of values

for the attributes (fields) identified.

______________________________________________

______________________________________________

______________________________________________

______________________________________________

______________________________________________


Proper name selection

• Computer scientists have long recognized the critical importance ofchoosing correct names for the elements of a program.

• Computer scientists also recognize that a set of well-namedprogramming elements shows a mastery of the logic and nature ofthe underlying computation.

• An element is well named if the name descriptively and correctlyreflects the central essence of the element.

• Proper naming thus enables a computer scientist to more clearlyreason about the algorithm and data of the program.

• Poorly named program elements reflect a confused understanding ofthe elements and also make clear-headed reasoning more difficult.


✓ Appropriate choices of names are keystone for good style.

✓ Poor naming makes is difficult to understand (leads to confusion).

• In the Figure: Importance of naming, Algorithm2 uses appropriate

names.


Algorithm 1

1. Get a,b,c

2. If a<24 && b<60 && c<60

Then Return true

Else Return false

Algorithm 2

1. Get hours, minutes, seconds

2. If hours<24 && minutes<60

&& seconds<60

Then Return true

Else Return false

Figure: Importance of naming

• Two algorithms for computing cost of gas filling is given in

Algorithm 1 (Version 1)and Algorithm 2 (Version 2).

✓ Can you comment on the names in terms of their readability?Which

algorithm follows proper naming conventions?


1. C 3.75

2. Size 10

3. Money Size * C

Algorithm 1

1. INRPerGallon 3.75

2. TankCapacity 10

3. INRToFill TankCapacity *

INRPerGallon

Algorithm 2

Figure: Version #1 Figure: Version #2

• An algorithm using an exchange rate of 10 to determine the BRL

that corresponds with US$3.75 is given in Figure: Concurrency

conversion.

✓ What will happen in the above examples if descriptive names are

replaced with names like x,y,z etc.


1. USD 3.75

2. ExchangeRate 10

3. BRL USD * ExchangeRate

Figure: Currency conversion

✓Given that width = 17, height = 2.0 and delimiter = ‘ . ’

✓For each of the following expressions, find the value of the expression

and type (of the value of the expression) (number, string,boolean)

1. width/2

2. width/2.0

3. height/3

4. 1 + 2 * 5

5. delimiter * 5


Given that width = 17, height = 2.0, and delimiter = '.'

For each of the following expressions, can you find the

value of the expression

type (of the value of the expression)

width/2 = 17/2 ------------- 8(Integer)

width/2.0 =17.0/2.0 ----------8.5 (Float)

height/3 =2.0/3 -----------0.66 (Float)

1 + 2 * 5 ---------11

delimiter * 5 -------ASCII value of ‘.’ (46)* 5 = 230

Ability to

• Understand

• Execute

• Evaluate

• Create algorithms

Algorithmic thinking


ALGORITHM

• An algorithm is a sequence of finite instructions,often used for calculation and data processing.

• It is an effective, step-by-step method of solving aproblem.

• A method in which we write a list of well-definedinstructions for completing a task.

• It will start from an initial state, proceed through awell-defined series of successive states, eventuallyterminating in an end-state.


CHARACTERISTICS


1. Finiteness. An algorithm must always terminate

after a finite number of steps.

2. Definiteness. Each step of an algorithm must be

precisely defined; the actions to be carried out must

be unambiguously specified for each case.

3. Input.An algorithm has zero or more inputs.

4.Output. An algorithm has at least one desirable

output.

5. Effectiveness. All operations to be performed in the

algorithm must be sufficiently basic.

Problems (Tasks), Algorithms, Programs



Expressing Algorithms

Testing the correctness of algorithms


Test the algorithm by choosing different

sets of input values, carrying out the

algorithm (tracing the computational

states), and checking to see if the resulting

solution does, in fact, work.

Facebook registration

• To log in to facebook account we first enter the facbook URL

www.facebook.com in our browser like Google, Firefox, Safari,

Internet Explorer etc. This request is sent to the facebook

server and it responds by sending us the home page of facebook.

• Next, we enter our registered Email ID and Password and click

the Login button.

• Then our login credential is checked. If it is correct, we are

show our profile. On the other hand, if the login credential is

wrong then an error occurs and we are prompted to re-enter

our Email ID and Password.

1. Start

2. Enter www.facebook.com in your browser. (Input)

3. facebook Home page loads (PROCESS)

4. Enter your Email ID and Password (Input)

5. Is Email ID and Password Valid? (DECISION)

then Display facebook Account (Output)

else Log in error (PROCESS) and go to step 3

6. Stop

Area and circumference of circle

Step 1 : Start

Step 2 : Set the value of pi to Pi

Step 3 : Read radius r

Step 4 : Compute area and circumference

Step 5 : Display area and circumference

Step 6 : Stop


Step 1 : Start

Step 2 : Set Pi =3.14

Step 3 : Read r

Step 4 : Area=Pi*r*r

Step 5: Circumference=2*Pi*r


Step 7 : Stop


Step 1 : Start

Step 2 : Declare Pi, r,Area,Circumference

Step 3 : Set Pi =3.14

Step 4 : Read r

Step 5 : Area=Pi*r*r

Step 6: Circumference=2*Pi*r


Step 8 : Stop

Calculate the Interest of a Bank Deposit

Step 1: Start

Step 2: Declare Amount, Years, Rate, Interest

Step 3: Read Amount

Step 4: Read Years

Step 5: Read Rate

Step 6: Interest=Amount*Years*Rate/100

Step 7: Print Interest

Step 8: Stop

Write an Algorithm for

Step1: Start

Step2: Read/input x

Step3: If (x<0) then f =-x

Step4: If x (>=0) then f =x

Step5: Print f

Step6: Stop


Determine whether a number is Even or Odd

Step 1: Start

Step 2: Declare N, Remainder

Step 3: Read N

Step 4: Remainder = N modulo 2

Step 5: If (Remainder is equal to 0)

then answer = “Number is even”

else answer = “Number is odd”

Step 6: Print answer

Step 7: Stop

Determine Whether A Student Passed the Exam or Not

Step 1: Start

Step 2: Declare M1,M2,M3,M4,average_grade

Step 3: Input grades of 4 courses M1, M2, M3, M4

Step 4: average_grade=(M1+M2+M3+M4)/4

Step 5: If (average_ grade < 60 )

then print "FAIL”

else print "PASS”

Step 6: stop

1. Start

2. Get cash amount .

3.Set Hs (hundreds) and Fhs (five hundreds) to 0.

4. If (amount < 500)

Then Hs = amount/100

Else Fhs = amount / 500

Hs = (amount mod 500) / 100

5. Display the amount, Fhs and Hs.

6. Stop

Denomination while dispensing cash (assuming

availability of only 100 and 500 Rs. Notes)


An algorithm with a natural number, n, as its input , to

calculate : S = ½ + ¼ + ... +1/n

1. Start

2. Read n

3. Set i =2 , S = 0

4. While ( i<=n)

4.1 S= S + (1/i )

4.2 i ← i + 2

5. Display S

6. Stop


Multiway selection

IF decision_1

THEN sequence_1

ELSE IF decision_2

THEN sequence_2

ELSE IF decision_3

THEN sequence_3

ELSE sequence_4

Determine Largest of 3 Numbers

Step 1: StartStep 2: Declare N1,N2,N3, MAXStep 3: Input N1, N2, N3Step 4: if (N1>N2)

then if (N1>N3) then MAX N1else MAX N3

endifelse if (N2>N3)

then MAX N2else MAX N3

endifendif

Step 5: Print “The largest number is”, MAXStep 6: Stop

Read an employee name, overtime hours

worked , hours absent and determine the

bonus payment.

Bonus Schedule

OVERTIME – (2/3)*ABSENT Payment

>40 hours

>30 but 40 hours

>20 but 30 hours

>10 but 20 hours

10 hours

50

40

30

20

10

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


then PAYMENT = 30


then PAYMENT = 20

else PAYMENT = 10

endif

Step 3: Print “Bonus for”, NAME “is inr”, PAYMENT

Take as input the user’s bank account balance and

the type and level of account they have. Based on

this information and the below rate table, determine

the interest rate .

Sum of 5 numbers

1. Start

2. Declare sum, count, num

3. Set sum = 0, count = 0 (Initialize)

4. Enter num (Input /Read )

5. Find sum + num and assign it to sum (Compute)

6. Increment count by 1 (Compute)

7. If (count < 5) (Decision)

then go to step 3 (Repeat)

else Print sum (Output / Display)

8. Stop

Sum of 5 numbers

1. Start


3. Set sum = 0, count = 0 (Initialize)

4. Enter num (Input /Read )

5. sum= sum + num (Compute)

6. count = count +1 (Compute)

7. If (count < 5) (Decision)

then go to step 3 (Repeat)

else Print sum (Output / Display)

8. Stop

Sum of 5 numbers

1. Start


3. Set sum = 0, count = 0

4. While (count < 5)

4.1 Enter num

4.2 sum= sum +num

4.3 count = count +1

5. Print sum

6. Stop

Sum of n numbers

1. Start

2. Declare sum, count, num,n

3. Set sum = 0, count = 0

4. While (count < n)

4.1 Enter num

4.2 sum= sum +num

4.3 count = count +1

5. Print sum

6. Stop

0! = 1

1! = 1 = 0! x 1

2! = 1 x 2 = 1! x 2

3! = 1 x 2 x 3 = 2! x 3

4! = 1 x 2 x 3 x 4 = 3! x 4

5! = 1 x 2 x 3 x 4 x 5 = 4! x 5

6! = 1 x 2 x 3 x 4 x 5 x 6 = 5! x 6

✓ Do you see a pattern emerging?

✓ Can you write an algorithm employing this pattern?

p = 1 = 0!

p = p x 1 = 1!

p = p x 2 = 2!

p = p x 3 = 3!

p = p x 4 = 4!

p = p x 5 = 5!

p = p x 6 = 6!

A Refresher on Factorial


p = 1 = 0!

p = p (whose value now is 0!) x 1 = 1!






The pattern!!


Factorial of a given number

1. Start

2. Set fact=1 , i =1

3. Read n

4. While (i < = n)

3.1 fact = fact * i

3.2 i = i +1

5. Print fact

6. Stop

Sum all the even numbers between 1 and 20 inclusive

and then displays the sum.

Step1 : Start

Step 2: Declare sum, count

Step 3: Set sum = 0, count = 1

Step 4: REPEAT

4.1 IF (count mod 2 is equal to 0)

THEN sum = sum + count

4.2 count = count + 1

UNTIL count > 20

Step 5: DISPLAY sum

Step 6: Stop

Read integer, check if it is –1, if so quit. If not, add this

number to the sum and repeat read.

Step 1: StartStep 2: Declare sum, xStep 3: Set sum = 0Step 4: Read xStep 5: While (x != -1) do

5.a : sum = sum + x5.b: Read next x

Step 6: Stop

Consider the previous example set.

Three situations are possible

• 2nd number can be less than the temporary maximum number.

• It could be equal to the temp. max. no.

• It could be greater than the temp. max. no.

Situations 1 & 2, the temp. max. no. is unchanged. Situation 3, the

2nd number becomes the new temp. max. no.

This has to be repeated till the end of the set.

8 136211971556

Find maximum number in a set of numbers


1.Get an array a[0,...n-1] of n elements where n ≥ 1.

2. Set temporary maximum max to first array element i.e. a[0].

3. While less than n array elements have been considered repeatedly

do

a)If next element greater than current maximum then assign it

to max.

4. Return the maximum max for the given array.

Algorithm to find maximum number


What has been described?

• Naming and importance of naming

• Characteristics of algorithm

• Algorithms for various problems using combinations of

control structures

Credits

•Programming Languages,2nd edition,Tucker and Noonan

•www.cse.msu.edu/ Organization of Programming Languages-Cheng (Fall 2004)

•Computing Without Computers,A Gentle Introduction to Computer

• Programming,Data Structures and Algorithms,Version 0.15,Paul Curzon

•Google images

•http://courses.cs.vt.edu/cs2104/Fall12/notes/T16_Algorithms.pdf

•http://bisma.in/algorithm-and-its-characteristics/


Documents

Naming, Algorithms#1 CTPS 2018 · 2019. 5. 20. · 1. Start 2. Declare sum, count, num 3. Set sum = 0, count = 0 (Initialize) 4. Enter num (Input /Read ) 5. Find sum + num and assign