Cs 1114 - lecture-9

Instructor : Muhammad Haris

All Rights Reserved to Department of Computer Science – GCU Lahore

Programming Fundamentals

Assignment-1 SolutionPeriod Meaning

March 21 – April 19 If Month is 3 thenDay must be 21st or aboveOr if Month is 4 thenDay must be 19th or below

Programming Fundamentals | Lecture-9 2

(m == 3 AND d >= 21)OR

(m == 4 AND d <= 19)

Wrong Decision Rules


m == 3 OR

m == 4

m == 4 OR

m == 5

DISPLAY “Aries”

Wrong Decision Rules


(m == 3 AND d >= 21 AND d <= 31)

(m == 4 AND d >= 20 AND d <= 30)

Less Better Approach


m == 3

m == 4 Further rules

Lessons from Previous Lecture If we have to multiply/add etc. series of

numbers using a computer program, we can make it happen by multiplying/adding etc. 2 numbers at a time and then multiplying its result by the next number in the next repetition and we keep on doing so until we get the required resultResult from calculation in previous repetition

is used in the next repetition


Lessons from Previous Lecture To repeatedly do a task we need to do

the following:


count = count + 1count < n

count = 0

Yes

1 or more steps

Lessons from Previous Lecture The original purpose of count is to keep

record of number of repetitionsHence, it’s value changes like that

○ 1 2 3 4 5 …...n

However, if needed, count can be used in a calculationE.g., sum = sum + count

○ Note that doing so doesn’t affect the value of count (it just uses it)


Lessons from Previous Lecture Key steps to follow for repetition

Identify what you have to do repeatedly○ If it is a calculation or something else which is

not fixed, analyze which part of it is changing and how it is changingE.g., sum = sum + _fact = fact * _

○ Can you make use of count for the changing part or do you need some other field

Identify how many times you have to repeat it


Another Example

Find sum of first 5 even numbersThere are two ways to do this

○ Make use of count OR○ Use a special field instead of count

What about sum of first ‘n’ even numbers


Sum of first 5 even numbers


START

sum = 0

count = count + 1

STOP

count < 5

count = 0

DISPLAY sum

YesNo

sum = sum + count + count

Alternative


START

sum = 0

count = count + 1

STOP

count < 5

count = 0

DISPLAY sum

YesNo

sum = sum + even

even = 0

even = even + 2

Another Example

Find sum of first n odd numbersSimilarly, two ways to do it


Sum of first n odd numbers


START

sum = 0

count = count + 1

STOP

count < n

count = 0

DISPLAY sum

YesNo

sum = sum + count + count - 1

Alternative


START

sum = 0

count = count + 1

STOP

count < 5

count = 0

DISPLAY sum

YesNo

sum = sum + odd

odd = -1

odd = odd + 2

Consider This

Display first n even numbersHow it is different from the earlier example?

If we don’t need to use the result of previous calculation, we don’t need to save it


Display first n even numbers


START

count = count + 1

STOP

count < 5

count = 0

YesNo

DISPLAY even

even = 0

even = even + 2

Another Example

Display “multiplication table” of a number up to 10Do we need to save the result of calculation

in every repetition?○ Let’s see the solution


Table of a number up to 10


START

count = count + 1

STOP

count < 10

count = 0

YesNo

DISPLAY num * count

READ num

Another Example

Find sum of 5 natural numbers starting from 2626 + 27 + 28 +29 + 30



START

sum = 0

count = count + 1

STOP

count < 5

count = 0

DISPLAY sum

YesNo

sum = sum + count + 25

Testing


Repetition-1 Repetition-2 Repetition-3 Repetition-4 Repetition-5

decision (count < 5) 0 < 5 1 < 5 2 < 5 3 < 5 4 < 5

count = count + 1 1 = 0 + 1 2 = 1 + 1 3 = 2 + 1 4 = 3 + 1 5 = 4 + 1

sum = sum + count +2526 =

0 + (1 + 25) 53 =

26 + (2 + 25)81 =

53 + (3 + 25)110 =

81 + (4 + 25)140 =

110 + (5 + 25)

count = 0 sum = 0

A Challenging Task

Display the following series for first n numbers in this series1 2 4 7 11 16 ……



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Cs 1114 - lecture-9