Finding the bug in code – practice for Years 8–9

Sample questions on Finding the bug in code with the right answer and a worked solution, from easy to hard. In the Pickles Academy app a child gets new questions of the same kind every time, so they can't just learn the answers by heart.

Subject

Computing

Year

Years 8–9

Curriculum area

Algorithms and programming

Question types: Which line has the bug?

Sample questions

1. Question 1 Easy

   The program should print the sum of the numbers from 1 to 6, but it prints 0. Which line has the bug?

   1n = 6
   2s = 0
   3for i in range(1, n + 1):
   4    s = s * i
   5print(s)
   

   1. A) line 1
   2. B) line 2
   3. C) line 3
   4. D) line 4
   5. E) line 5
   Show the solution

   Answer: D) line 4

   How it works: Line 4 is wrong; it should be: s = s + i. Then the program prints 21.

2. Question 2 Normal

   The program should print the sum of the numbers from 1 to 6, but it prints 15. Which line has the bug?

   1n = 6
   2s = 0
   3for i in range(1, n):
   4    s = s + i
   5print(s)
   

   1. A) line 1
   2. B) line 2
   3. C) line 3
   4. D) line 4
   5. E) line 5
   Show the solution

   Answer: C) line 3

   How it works: Line 3 is wrong; it should be: for i in range(1, n + 1):. Then the program prints 21.

3. Question 3 Hard

   The program should print the sum of the even numbers from 2 to 10, but it prints 25. Which line has the bug?

   1n = 10
   2s = 0
   3for i in range(1, n + 1, 2):
   4    s = s + i
   5print(s)
   

   1. A) line 1
   2. B) line 2
   3. C) line 3
   4. D) line 4
   5. E) line 5
   Show the solution

   Answer: C) line 3

   How it works: Line 3 is wrong; it should be: for i in range(2, n + 1, 2):. Then the program prints 30.

All Computing topics