Answers

F2.2 Selection: if

Decisions and loops · GCSE · OCR J277 2.2.1, AQA 8525 3.2.4, Edexcel 1CP2 6.5.2 · about 12 min

What this lesson is about

Relational operators, and a block that runs only when a condition is true.

• Questions with a yes-or-no answer
• if: run a block only when the answer is True
• Comparing text
• The answer can come from a variable

Questions 9 marks in all

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

   speed = 40
   if speed > 50:
       print("fast")
   if speed > 30:
       print("medium")
   if speed > 10:
       print("slow")
   print("checked")

   Answer:

   medium
   slow
   checked

   Three separate ifs are each checked. 40 > 50 is False; 40 > 30 and 40 > 10 are both True.

2. [1 mark]What is the difference between = and ==?

   1. A= stores a value, == asks whether two values are equal
   2. BThey mean the same
   3. C== stores a value, = compares
   4. D= is for text, == for numbers
   Answer: A. Mixing them up is one of the most common early mistakes.

3. [1 mark]Which comparison means "is not equal to"?

   1. A!=
   2. B<>
   3. C=!
   4. Dnot=
   Answer: A. != is not equal. The others are not Python.

4. [1 mark]What does this program print?

   d = 25
   print(d < 30)
   print(d >= 30)

   Answer:

   True
   False

   A comparison gives True or False.

5. [1 mark]What happens to the block under an if when the question is False?

   1. AIt is skipped, and the program carries on below it
   2. BIt runs anyway
   3. CThe program stops
   4. DPython shows an error
   Answer: A. The block runs only when the answer is True.

6. [1 mark]What does this program print?

   x = 7
   if x % 2 == 0:
       print("even")
   print("done")

   Answer:

   done

   7 % 2 is 1, so the question is False and the block is skipped.

7. [1 mark]What does this program print?

   answer = "Yes"
   if answer == "yes":
       print("driving")
   print("done")

   Answer:

   done

   "Yes" with a capital Y is a different string from "yes", so the condition is False.

8. [1 mark]d is exactly 40. Which condition is True?

   1. Ad <= 40
   2. Bd < 40
   3. Cd > 40
   4. Dd != 40
   Answer: A. Only the or-equal version includes 40 itself. The edge value is where selection mistakes hide.

9. [1 mark]How does AQA pseudo-code write "is equal to"?

   1. A=
   2. B==
   3. C===
   4. DEQUALS
   Answer: A. AQA pseudo-code uses a single = for equality (and ← for assignment). Python uses ==.

The task: near or far

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

forward(50, distance=20)
d = distance()
if d < 40:
    print("near")

from bugbot import *
connect()
forward(50, distance=20)
d = distance()
if d < 40:
    print('near')
    led('red')
if d >= 40:
    print('far')
    led('green')