Python Conditionals and Loops

Objective Type Questions

Question 1

Which of the following are invalid conditional statements of Python?

1. IF
2. Test if
3. if-else
4. if-elif
5. if
6. if-elif-else

Answer

IF and Test if

Reason — IF and Test if are invalid conditional statements of Python.

Question 2

Which of the following is/are not a valid Python loop ?

1. for
2. while
3. iter
4. repeat

Answer

iter, repeat

Reason — iter and repeat are not valid Python loop. for and while are valid loop statements.

Question 3

Which of the following is used to define a block of code (e.g., body of if or body of a loop) in Python ?

1. { }
2. ( )
3. indentation
4. Quotation

Answer

indentation

Reason — Indentation is used to define a block of code in Python.

Question 4

What is the output of following code ?

if None :
    print "Up"
else:   
    print "Down"

1. Up
2. Down
3. No output
4. Up Down

Answer

Down

Reason — Since None is treated as false, the if condition results in false. The block of if will be ignored and the else block will be executed and Down will be printed on the output screen.

Question 5

What will be the output of following code ?

for i in range(1) : 
    print i

1. 0
2. 1
3. No output
4. Error in code

Answer

0

Reason — The range(n) function generates a list as [0, 1, 2..., n - 1]. Thus, the range(1) function will generate a list as [0]. Thus the for loop will execute only one time and print 0 on the output terminal.

Question 6

What will the output of following code ?

for i in range(1, 0) :
    print i

1. 0
2. 1
3. No output
4. Error in code

Answer

No output

Reason — The function range(1, 0) will return return an empty list [] as no number falls in the arithmetic progression beginning with 1 and ending with 0. Thus, the for loop will not execute even once and hence, no output will be generated on the output screen.

Question 7

What is the output of following code ?

while 3 >= 3 :
    print 3

1. 3 is printed once
2. 3 is printed three times
3. 3 is printed infinitely until program is closed
4. Error in code

Answer

3 is printed infinitely until program is closed

Reason — Since the given condition (3 >= 3) will always remain true, the while loop will execute indefinitely and keep on printing 3 on the output screen till the program is closed.

Theoretical Questions

Question 1

What are selection statements ? How are they useful ?

Answer

A statement that carries out a set of instructions depending upon a condition's result is known as a selection or conditional statement. Python provides selection statements in the form of if and if-else statements.

These statements enable a program to carry out a set of instructions depending upon a condition's result. For example,

num = 5
if num >= 0 :
    print "Positive"
else :
    print "Negative"

Question 2

What are looping statements ? How are they useful ?

Answer

A statement that allows a set of instructions to be performed repeatedly is known as a looping or iteration statement. Python provides looping statements in the form of for and while loop.

These statements enable a program to perform a set of instructions repeatedly. For example,

num = 3
while num > 0 :
    print num
    num = num - 1

Question 3

Differentiate between if and if-else statements.

Answer

Difference between if and if-else statements in Python:

Question 4

Differentiate between for and while statements.

Answer

Difference between for and while statements in Python:

Question 5(a)

Rewrite the following code fragments using for loop

while num > 0 :
    print num % 10 
    num = num/10

Answer

l = [1]
for x in l:
    l.append(x + 1)
    if num <= 0:
        break
    print (num % 10)
    num = num/10

Question 5(b)

Rewrite the following code fragments using for loop

i = 100
while (i > 0) :
    print i
    i -= 3

Answer

for i in range(100, 0, -3) :
    print (i)

Question 6

What is following code doing ? What would it print for input as 3 ?

n = input( "Enter an integer:" )
if n < 1 :
    print "invalid value"
else :
    for i in range(1, n + 1): 
        print i * i

Answer

The code will print the square of each number from 1 till the number given as input by the user if the input value is greater than 0. Output of the code for input as 3 is shown below:

Enter an integer:3
1
4
9

Question 7(a)

Rewrite following code fragments using while loops

min = 0 
max = num 
if num < 0 :
    min = num 
    max = 0 
# compute sum of integers from min to max 
for i in range(min, max + 1): 
    sum += i

Answer

min = 0
max = num
if num < 0 :
    min = num
    max = 0
# compute sum of integers from min to max 
i = min
while i <= max:
    sum += i
    i += 1

Question 7(b)

Rewrite following code fragments using while loops

for i in range(1, 16) : 
    if i % 3 == 0 : 
        print i 

Answer

i = 1
while i < 16:
    if i % 3 == 0 :
        print (i)
    i += 1

Question 8(i)

Write a short program to print the following series :

1 4 7 10 ........... 40.

Answer

Solution

for i in range(1, 41, 3) :
    print(i, end = ' ')

Output

1 4 7 10 13 16 19 22 25 28 31 34 37 40

Question 8(ii)

Write a short program to print the following series :

1 -4 7 -10 .......... -40

Answer

Solution

x = 1
for i in range(1, 41, 3) :
    print(i * x, end = ' ')
    x *= -1

Output

1 -4 7 -10 13 -16 19 -22 25 -28 31 -34 37 -40

Question 9(a)

Predict the output of the following code fragments :

count = 0 
while count < 10: 
    print "Hello" 
    count += 1 

Answer

Output

Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello

Explanation

The while loop executes 10 times so "Hello" is printed 10 times.

Question 9(b)

Predict the output of the following code fragments :

x = 10 
y = 0 
while x > y: 
    print x, y 
    x = x — 1 
    y = y + 1 

Answer

Output

10 0
9 1
8 2
7 3
6 4

Explanation

Question 10

What will be output of the following code if the user enters Principal amount as 20000 and Time as 10 years.

#Considering Python 2.7 
P = input("Enter Principal amount:") 
T = input("Enter Time:") 
if T > 10: 
SI = P*T*10/100 
else: 
SI = P*T*15/100 
print("Simple Interest = ", SI) 

Answer

Output

Enter Principal amount:20000
Enter Time:10
Simple Interest =  30000

Explanation

This Python program calculates the Simple Interest (SI) based on the given Principal amount (P) and Time (T) values. For time value of more than 10 years, the program takes the rate of interest as 10% and for 10 years or less it takes the rate of interest as 15%.

Question 11

Write a Python script that asks the user to enter a length in centimetres. If the user enters a negative length, the program should tell the user that the entry is invalid. Otherwise, the program should convert the length to inches and print out the result. There are 2.54 centimetres in an inch.

Answer

Solution

len = int(input("Enter length in cm: "))
if len < 0:
    print("Invalid input")
else:
    inch = len / 2.54
    print(len, "centimetres is equal to", inch, "inches")

Output

Enter length in cm: 150
150 centimetres is equal to 59.05511811023622 inches

Question 12

Write a program that asks the user for two numbers and prints Close if the numbers are within .001 of each other and Not close otherwise.

Answer

Output

Enter first number: 10.12345
Enter second number: 10.12354
Close

Question 13

Write a short program to print first n odd numbers in descending order.

Answer

Solution

n = int(input("Enter n: "))
x = n * 2 - 1

for i in range(x, 0, -2) :
    print(i)

Output

Enter n: 5
9
7
5
3
1

Application Oriented Questions

Question 1

Consider the following code fragment :

while
    n = 3
    print n == 3

(a) What will be the output of above code ?

(b) What is the reason behind this output ?

Answer

(a) The given code will generate a syntax error.

(b) The condition of while and colon after that is missing. Thus a syntax error is generated.

Question 2

Consider the following code fragment :

n = 3
while n == 3
    print n
n = n - 1

(a) What will be the output of above code?

(b) What is the reason behind this output ?

(c) What change/corrections will you make to above code to make it print some output ?

Answer

(a) The given code will generate a syntax error.

(b) The syntax of while statement has a colon after the condition which is missing in the given code. Thus, a syntax error is generated.

(c) The following changes must be made to the code to print some output:

n = 3
while n == 3 :
    print (n)
    n = n - 1

The code given above will generate the following output:

3