Page 310 - Computer Science V2.0 Class 11

11.4.3 for Statement Vs while Statement
We have already learnt that each of the for and while statements is used for looping. We have already used a
for statement to develop a function that finds the factorial of a number. Now we ask the question: can we
compute the factorial of a number using a while statement? Of course, we can, as illustrated in program 11.7.
A more serious question to ask is whether we should write a function to compute the factorial of a number using a
while statement. The answer to this question is a resounding "NO." When all we need to do is count up or down, a
certain number of times, a for statement should be the natural choice because that is how we think. For example,
while moderating the results of an examination, a teacher might tell an official: Increase each student's marks by two.
In contrast, imagine the teacher telling the official: while there are students in the class, increase a student's marks
by two. Repeat the process of checking and updating the student's marks until there are no more students left. How
incomprehensible is the second version? The same thing applies to computer programs. As the programs developed
by a programmer need to be maintained. To make the programs readable, we need to be judicious in our choice of
the control structures (or in fact, any syntactic structure), as indiscriminate use of the language's syntax makes the
programs unreadable.

Program 11.7 To compute factorial of a number using a while statement.
01 def factorial(num):
02 '''
03 Objective: To find factorial of a number
04 Inputs:
05 num : the number whose factorial is to be computed
06 Return value:
07 product : factorial of num
08 '''
09
10 product = 1
11 count = 2
12 while(count <= num ):
13 product = product * count
14 count = count + 1
15 return product
16 number=int(input('Enter the number for factorial '))
17 print(factorial(number))
Sample Output:
>>> Enter the number for factorial 6
720

What will be the output produced when the following function is invoked with the argument 4.
def myFactorial(num):
'''
Objective: To find factorial of a number
Inputs:
num : the number whose factorial is to be computed
Return value:
product : factorial of num
'''
product = 1
count = 1
while(count <= num ):
product = product * num
count = count + 1
return product

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