Worksheet

A1.1 Data types and programming constructs

Programming techniques and object-oriented programming · A level · OCR H446 2.2.1, AQA 7517 4.1.1.1, Eduqas A500QS 1.4 · about 20 min

What this lesson is about

The A level data types, references and user-defined types, constants, and definite and indefinite iteration.

• The types you need to know
• References: two names, one value
• User-defined types
• Declaration, assignment and constants
• Iteration: definite and indefinite

Questions 6 marks in all

1. [1 mark]A variable holds the location in memory where a list of readings is stored, rather than the readings themselves. What is its data type?

   1. APointer/reference
   2. BArray
   3. CRecord
   4. DInteger

2. [1 mark]What does this program print?

   a = [1, 2]
   b = a
   b.append(3)
   c = list(a)
   c.append(4)
   print(a, len(c))

3. [1 mark]A loop has its condition tested at the end. What is always true of it?

   1. AIts body runs at least once
   2. BIts body may run zero times
   3. CIt is definite iteration
   4. DIt cannot use a Boolean condition

4. [1 mark]Which are advantages of using a named constant such as SAFE_CM instead of typing 25 wherever it is needed?

   Tick every answer that is true.

   1. AThe value only has to be changed in one place
   2. BThe name explains what the value means
   3. CIt cannot be changed by mistake while the program runs, in a language that enforces constants
   4. DIt makes the program run in less memory

5. [1 mark]A robot must repeat 'drive 5 cm' until the wall is 25 cm away. The number of repeats is not known in advance. What kind of iteration is this?

   1. AIndefinite iteration
   2. BDefinite iteration
   3. CRecursion
   4. DSelection

6. [1 mark]Python has no character type. What type does it use to store a single character such as "F"? Give the Python type name.

The task: readings as a record type

Define a record type Reading with namedtuple and three fields: heading (an integer, 0, 90, 180 or 270), cm (the real number distance() returns) and clear (a Boolean, True when cm is more than the constant CLEAR_CM). Declare CLEAR_CM = 40 as a constant and use the name, not 40, in the comparison. The robot starts facing heading 0. Take a reading, store it in an array, turn right 90 degrees, and repeat until there are four readings and the robot faces its starting direction. Then print each record with print(r), which shows Reading(heading=90, cm=51.0, clear=True), and finally print clear directions: <n>, the number of records whose clear field is True.

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

from collections import namedtuple

Reading = namedtuple("Reading", ["heading", "cm", "clear"])

survey = []
# take four readings, one every 90 degrees

print("clear directions:", 0)

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/a1-1-data-types-and-constructs/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Add a fourth field, taken, holding the time of the reading from clock(). What type is it?
2. Rewrite the survey loop as a condition-at-the-end loop that stops when the robot has turned a full circle.
3. Try r.cm = 0 on one of your records. What happens, and why might that be useful for sensor data?