Fundamental Programming Lect 3

Instructor : Muhammad HarisAll Rights Reserved to Department of Computer Science – GCU Lahore
Programming Fundamentals

Tasks (from previous lecture)
 Calculate area of a rectangle
area = base × height
 Find Cube of a Number
 Calculate Marks Percentage
(marks obtained / total marks) × 100
 Calculate Sales Tax
amount × (tax percent / 100)
 Find “no. of minutes” and “no. of seconds”
for given “no of years”
Programming Fundamentals | Lecture-3 2

Power of Computer Programs
 Once given the input
They perform the instructions (or no. of
steps as instructed by the programmer)
themselves and give the desired output
○ No matter how complex the problem is and
how long they have to work on it
Now We Will Further Explore Their Power

Consider this Problem
 Find absolute value after subtracting
one number from another
Difference = number1 – number2

Difference of Two numbers
START
READ number1, number2
difference = number1 - number2
DISPLAY difference
STOP
Will result in a negative
value if number1 is
smaller than number2

Is This Solution Correct?
START
DISPLAY difference
STOP
difference = difference * -1

Analyze the Problem
 There exists two conditions
Condition-1
○ Difference is positive
Condition-2
○ Difference is negative

What is to be Done?
 There exists two conditions
Condition-1
○ Difference is positive
Do not do any conversion, because value is already
positive
Condition-2
○ Difference is negative
Convert it into a positive value by multiplying it by “-1”

Should we design
two different solutions?
9Programming Fundamentals | Lecture-1

What is Required?
 Need to design a solution in such a way
which can decide for itself whether to
multiply the difference by “-1” or not (by
checking the value of difference)
 The graphical shapes which we have
learned so far are insufficient to provide
this kind of “decision making”

Decision Box
Decision
Rule
YesNo
Always in the form
whose answer is
“Yes” or “No”

START
DISPLAY difference
STOP
difference = difference * -1
difference < 0
YesNo

Power of Computers
 Decision Making
Programmers can instruct computers to
make decisions while solving a problem
○ As the complexity of problems increases,
decision making process become more
extensive
This way computers prove very useful by
performing laborious tasks of decision
making

Another Example
 Find smaller of two numbers
 Input
number1
number2
 Output
smaller
 Processing
Compare the numbers with each other and
decide which one is smaller

START
DISPLAY smaller
STOP
smaller = number1
number1 < number2
YesNo
smaller = number2

Alternative
START
STOP
DISPLAY number1
number1 < number2
YesNo
DISPLAY number2

Comparison Operators
 < (less than)
 > (greater than)
 <= (less than equal to)
 >= (greater than equal to)
 == (equal to)
 != (not equal to)

Output a Message
DISPLAY “This is a message”

Try it Yourself
 Find whether a number is negative or
not?
 Find whether two numbers are equal or
not?
 Multiply two numbers if their difference
is greater than 0

Some Keywords
 Look for these keywords in problem
statement in order to determine the
usage of decision box
If
If and only if
Whether

Tasks (to be done by next lecture)
 Find whether the sum of two numbers is
greater than 50
 Find whether the sum of two numbers is
greater than the third number?
 Divide a number by another if only if the
second number is not equal to “0”
 Determine whether a student is “passed” or
“failed” from his marks
A student securing marks less than 50 is
considered “failed”

BE PREPARED
FOR QUIZ
IN
NEXT LECTURE

Fundamental Programming Lect 3

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