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CBSE Class 12 Computer Science Question 58 of 68

Data Structures - I : Linear Lists — Question 14

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Question

Question 13

Find the Error. Consider the following code, which runs correctly at times but gives error at other times. Find the error and its reason.

Lst1 = [23, 34, 12, 77, 34, 26, 28, 93, 48, 69, 73, 23, 19, 88]
Lst2 = []
print("List1 originally is: ", Lst1) 
ch = int(input("Enter 1/2/3 and \
predict which operation was performed?")) 
if ch == 1:
   Lst1.append(100)
   Lst2.append(100)
elif ch == 2:
   print(Lst1.index(100)) 
   print(Lst2.index(100)) 
elif ch == 3:
   print(Lst1.pop())
   print(Lst2.pop())
Answer 
Lst1 = [23, 34, 12, 77, 34, 26, 28, 93, 48, 69, 73, 23, 19, 88]
Lst2 = []
print("List1 originally is: ", Lst1) 
ch = int(input("Enter 1/2/3 and \
predict which operation was performed?")) 
if ch == 1:
   Lst1.append(100)
   Lst2.append(100)
elif ch == 2:
   print(Lst1.index(100)) # Error 1
   print(Lst2.index(100)) # Error 2
elif ch == 3:
   print(Lst1.pop())
   print(Lst2.pop()) # Error 3

When the user selects option 1 (ch == 1), the code works correctly, i.e., it appends 100 to both Lst1 and Lst2 at the end. However, errors occur when the user selects option 2 (ch == 2) or option 3 (ch == 3). The errors are as follows:

  1. Error 1 — Attempting to find the index of 100 in the list Lst1 using Lst1.index(100), an error occurs because 100 is not present in Lst1.
  2. Error 2 — Attempting to find the index of 100 in the list Lst2 using Lst2.index(100), an error occurs because 100 is not present in Lst2.
  3. Error 3 — Attempting to remove an item from an empty list Lst2 using Lst2.pop(), an error occurs because there are no items to remove.