Answers

F13.7 Where marks are lost

Exam preparation · GCSE · about 15 min

What this lesson is about

The ten commonest mistakes, checking on paper, and repairing a broken program.

• The ten that cost the most
• Checking a program on paper
• The slips that break code

Questions 5 marks in all

1. [1 mark]Which is the commonest way to lose marks you knew?

   1. AAnswering the wrong command word
   2. BBad spelling
   3. CWriting too neatly
   4. DUsing a pencil
   Answer: A. Describe answered with one word scores one of two.

2. [1 mark]What is wrong with setting a total to 0 inside a loop?

   1. AIt is reset every time round, so it never adds up
   2. BNothing
   3. CIt makes the loop slower
   4. DThe loop never ends
   Answer: A. It belongs before the loop.

3. [1 mark]if x = 5: will not run. Why?

   1. A= assigns; a comparison needs ==
   2. Bx must be a string
   3. CThere is no colon
   4. Dif needs brackets
   Answer: A. One of the commonest slips in a written answer.

4. [1 mark]Which three values should you trace a program with?

   1. AA normal one, a boundary one and an invalid one
   2. BThree normal ones
   3. COnly the boundary
   4. DOnly what the question gives
   Answer: A. That is the same test data you met in F6.3.

5. [1 mark]What does this program print?

   total = 0
   for n in range(1, 6):
       total = total + n
   print(total)

   Answer:

   15

   1 + 2 + 3 + 4 + 5 = 15.

The task: repair the program

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

for step in range(1, 4):
    total = 0
    forward(50, distance=15)
    total = total + 15
    print(f"step {step}: {total} cm")
print(f"total: {total} cm")
led(255, 0, 0)

from bugbot import *
connect()
total = 0
for step in range(1, 5):
    forward(50, distance=15)
    total = total + 15
    print(f"step {step}: {total} cm")
print(f"total: {total} cm")
led(0, 255, 0)