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F4.2 Parameters and return values

Functions and structured code · GCSE · OCR J277 2.2.3, AQA 8525 3.2.10, Edexcel 1CP2 6.6.2 · about 15 min

What this lesson is about

Information in and an answer out; procedures and functions.

• Parameters: information in
• Several parameters
• return: an answer out
• Printing is not returning
• Procedures and functions

Questions 7 marks in all

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

   def double(n):
       return n * 2
   
   print(double(4))
   print(double(10))

   Answer:

   8
   20

   return hands the value back to the call, and print shows it.

2. [1 mark]In def square(size):, what is size?

   1. AA parameter: it gets its value from the call
   2. BAn argument
   3. CA return value
   4. DA comment
   Answer: A. size is a parameter. In square(15), the 15 is the argument that gives it its value.

3. [1 mark]What does this program print?

   def greet(name, times):
       for i in range(times):
           print("hi", name)
   
   greet("Ada", 2)

   Answer:

   hi Ada
   hi Ada

   The values in the call fill the parameters in the same order.

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

   def double_print(n):
       print(n * 2)
   
   def double_return(n):
       return n * 2
   
   a = double_print(5)
   b = double_return(5)
   print(a, b)

   Answer:

   10
   None 10

   double_print shows 10 but returns nothing (None); double_return gives 10 back to be stored.

5. [1 mark]In area(20, 30), what are 20 and 30?

   1. AArguments
   2. BParameters
   3. CReturn values
   4. DLocal variables
   Answer: A. The values in a call are arguments; the names in the definition are parameters.

6. [1 mark]What is the difference between a function and a procedure?

   1. AA function returns a value; a procedure does not
   2. BA procedure has parameters; a function cannot
   3. CA function is written in capitals
   4. DThere is none in any language
   Answer: A. Python uses def for both; OCR's Reference Language has separate words, and AQA uses SUBROUTINE for both.

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

   def check(n):
       if n > 10:
           return "big"
       return "small"
   
   print(check(15), check(3))

   Answer:

   big small

   return ends the function straight away, so only one of the two returns runs for each call.

The task: any polygon

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

def polygon(sides, length):
    print("polygon with", sides, "sides")
    # drive it

polygon(5, 20)

from bugbot import *
connect()
def polygon(sides, length):
    print('polygon with', sides, 'sides')
    for i in range(sides):
        forward(60, distance=length)
        turn_right(30, angle=360 / sides)
polygon(5, 20)
polygon(3, 20)