Page 216 - Computer Science Class 11 Without Functions
P. 216
Program 9.6 Write a program to find reverse of the number.
01 '''
02 Objective: To find reverse of the number
03 Input:
04 num : number whose reverse has to be returned
05 Output: reverse of num
06 '''
07 num = int(input('Enter a number: '))
08 reverseNum = 0
09 while num > 0:
10 remainder = num % 10
11 reverseNum = reverseNum * 10 + remainder
12 num = num // 10
13 print('Reverse: ', reverseNum)
Sample Output:
>>> Enter a number: 1234
Reverse: 4321
As shown in the syntax for the while statement, it may include an optional else clause. It operates like the else
clause in a for statement, i.e., the else clause gets executed on a smooth exit from the while loop. However, if control
moves out of the while loop on execution of the break statement, the else clause is ignored.
Enter in loop
False
Condition
True
else block
Body
Encounter
no break
yes
Exit from loop
Fig 9.4
9.4.3 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 program 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 9.7. A more serious
question to ask is whether we should write a program 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.
214 Touchpad Computer Science-XI

