This document provides an overview of programming loops and different types of loops. It discusses while loops and for loops. While loops repeat code until a condition is met, and for loops iterate over a sequence a set number of times. It provides examples of infinite loops and how to end loops using break or changing conditions. Different types of loops are demonstrated including condition-controlled and count-controlled loops. Activities are included to practice different loop structures.

1. Going loopy……
Lesson 1

2. Starter activity
1. Use the internet to get an accurate, programming description of
programming loops
2. Write your answer on a post-it note
3. Repetition – code embedded within a loop repeats until a condition is
reached
Terminology Challenge :
What type of programming construct is this? s......, s........, i........
Iteration

3. Loops....
• Iteration
The act of repeating a process, either:
• Until a condition equates to True, or
• For a certain number of times

4. Learning objects
• What?
• Gain an understanding of different types of programming loops and how
these might be applied
• Understand the difference between count controlled and condition
controlled loops
• Identify how we end loops
• Apply iteration programming constructs to realistic scenarios
• Why?
• All programs include iteration of some form. Iteration is a fundamental
programming concept and needs to be implemented into your NEA.

5. Why include loops in our code?.......
• There may be times where we want to run some code over and over
again
• For example, entering a new password where the two inputs don’t
match.

6. Two types of Loops
Loop type Description
WHILE loop Uses a condition to determine whether or not the statements
should be executed. The statements are repeated until the
result of the condition equates to true.
e.g. while True
while goes <=10
while goes == True
FOR loop
Uses a variable as a counter; the counter is incremented each
time statements are repeated until it reaches a pre-set value.
For loops iterate over a given sequence
e.g. 5 times – for i in range(5)
My_friends = [‘Sarah’, ‘Jane’, ‘Sam’]
For i in range(0, len(My_friends))

7. Infinity ……..or not?
• Infinite loop – (forever) is where the program will loop continuously.
• Complete ‘Activity 1 – Infinite or not’

8. Task 1:
Explore how these loops
run and why some are
infinite and others aren’t
For each, tick the
appropriate column.

9. Answers
‘ ’
( )

10. Investigation
1. Investigate these
examples of iteration by
turning the pseudocode
into Python code.
• Iteration
The act of repeating a
process, either:
• Until a condition evaluates
to True or False, or
• Until a condition has
looped a certain number of
times
:
:
:
for x in range(1, y)




:
‘ ’
( )

11. Quick task …..infinite or not?

12. While loop ……Boolean expression TRUE
while True # means loop forever.
The while statement executes the loop body while the
Expression evaluates to (boolean) "true"
Infinite loop……how do we get
out of the loop?
Deconstruct : Boolean has one of two possible values true and false

13. Task – a loop to check length of a user’s name
while True
player input('Please enter your name: ')
IF player.length >=3 and player.length <=6:
OUTPUT "Accepted"
break
ELSE
OUTPUT "Please enter a username between 3 and 6 characters“
ENDIF
endwhile
len(player)
Using the Boolean
expression - ‘break’ will stop
the loop.

14. Complete code

15. Adaption of a Boolean loop
• We could assign the Boolean value to a variable.
• Then, test that variable to see if it is True or False.

16. Alternative condition controlled
Boolean while loop – use of a variable
happy = False
While happy equals False
happy input “Are you happy?”
if answer equals ‘yes’ then
output “You are happy”
happy = True
else if answer equals ‘no’ then
output “You are not happy”
happy = False
Extension:
Add an else statement to capture any other answer and set happy to False
Activity –
1. recreate this pseudocode as Python code
2. Alter the Boolean and replace with ‘yes’, ‘no’

17. Code
Infinite loop
Having a variable means
we can end the loop
Or keep it looping
Define the while
loop variable

18. Adapted – a loop to check length of a user’s
name
tries = True
while tries == True
player input('Please enter your name: ')
IF player.length >=3 and player.length <=6:
output "Accepted"
tries = False
ELSE
output "Please enter a username between 3 and 6 characters“
tries = True
end if
endwhile

19. Summary – glossary
• While loops are known as condition controlled iteration command
• A condition-controlled loop is used when it is not known how many
times iteration will need to occur.

20. Analysis – alternative while loop – count
controlled
• Analyse the two algorithms – re-create them in Python
• Why does one loop infinitely and the other one doesn’t?
Counter controlled condition
This program will increment
by 1 after every output
and eventually the condition
will evaluate to False and the
loop will end
Using < means the loop will
automatically end when it
reaches 9
Infinite

21. Task – adapt your ‘happy’ Code
Set the variable to 10
which means the
condition no longer
equates to TRUE – it
equates to FALSE
Define the while
loop variable
10
<10:
happy +1
Increment happy
0
Declare the variable & assign the value 0

22. Activity
• Using a while loop, create an entry login program that re-loops 4
times if the username entered is not equal to ‘1234’
• If the correct answer e..g ‘1234’ is entered, you need to break out of
the loop. To do this, choose a condition that is not less than or equal
to 4

23. Answers
Extension:
Adapt the code by using a
BOOLEAN value as the
condition

24. Activity - Adapt the pseudocode
• Create a program that:
• Gets username
• Gets password1
• Gets password2
• Checks to see if they match
• And exits if they do
• Re-loops if they don’t
• Only re-loops 4 times

25. Answer
What if they reach the
max attempts?

26. For loops – glossary
• Also a count controlled loop
• A count-controlled loop is used when the number of iterations to
occur is already known.

27. Another count controlled loop
A For loop iterates over a sequence of numbers
using the "range" function.
x =1, 2, 3, 4, 5
Once the program reaches the end of the range, the loop
ends.
is used when the number of iterations to occur is already known.
Stepper variable

28. Answers
What is wrong with this?

29. • Adapt this code to create a 10 times table

30. Next for loop...
• We don’t need a variable
for the start value
Extension:
• Add an if statement to jut
return the output if the
stepper contains 5.
01 for x = 1 to 21
02 OUTPUT ‘Number output is : x)

31. Plenary
What are the two types of Loops?
Loop type Description
WHILE loop Repeats a statement or group of statements while a given
condition is TRUE.
FOR loop
Executes a sequence of statements multiple times, until the
statement has been satisfied.
For loops iterate over a given sequence

32. Password check - The pseudocode for this
algorithm might look like this:
password = "blank“
WHILE password does not equal "ilovecomputing" THEN
INPUT password
OUTPUT "Password incorrect“
Recreate this as code
Extension – adapt the program – use a while loop to re-loop if password 1
and password2 are not the same

33. Exploring for loops’’
i Output i End of loop
1 1 False
3 3
5 5
9 9
11 11
13 13
15 15
17 17
19 19 True
i is 21 next – loop ends at 20
Review the code and complete the trace table.

34. Nested for loop can be used to iterate a
certain number of times
Extension:
1. Change the variables to something more meaningful
2. Explain what the purpose is of the nested loop.

35. Dice game
Import random
Create a dice game with
7 rounds
2 players roll per round
e.g. for player in range(1,3):
Dice roll is generated using random.randint(1,6)
e.g. dice_roll = random.randint(1,6)
print(‘You rolled……………. ‘, dice_roll)
Add up the dice roll score
e.g.
if player ==1:
p1score = p1score+dice_roll
else:
p2score = p2score+dice_roll

36. Dice game
Review the code:
What does the code
execute?
Extension:
Adapt this code so that
it has one while loop
and one for loop.

37. ART WORK
• A4 sheet
• Difference between count controlled and condition controlled lops
• Examples if infinite loops
• Example of the same loops but no longer infinite

38. Plenary
• https://create.kahoot.it/details/python-selection-iteration/250c536f-
6cd9-4707-8706-b682961be032

39. Revision
Define Selection
A condition is used to decide which instruction to execute next.
Score +=1 is only run if the IF condition is equates to true.
Define Iteration
A set of instructions that is repeated until a condition is met
e.g. The code in the repeat loop will be run several times (until
Position = 100).

40. Revision continued
String concatenation
• Joining together two or more values – could be strings, integers,
variables.
Casting
• Converting from one data type to another e.g. str(score) or
int(input())

41. Revision continued
Count controlled loop
For loop
• Repeat the code inside of them for a fixed number of times. The
number of times the code repeats will depend on the initial value,
end value and the step count.
• E.g. for i in range (0, 10, 2)

42. Revision continued
Condition controlled loop
• while loop
• Ctrolled by a condition at the start of a loop. Kepps going while the condition
wquates to true . Never run the ode inside og the loop if the condition is initially
false you get an infinite condition is always true.
e.g. tries = 4
While tries > 0: #this initially equates to true
if ans = ‘correct’:
tries = 0 #the condition will NOT equate to true if tries = 0
else:
tries = tries – 1 # the condition will equate to true if tries = 3,2,1

43. Test
• https://forms.gle/DaYGchV5vqeWPAEe6
• https://forms.gle/qEjZdGuU3fatcpiv7

44. PREDICT
Review this code and predict what will happen
answer = input("Is computer science your favourite subject? [Y/N] ")
agree = answer == "Y" #the logical statement answer == "Y" is evaluated, and the result of this is
assigned to the agree variable.
while not agree:
print("wrong answer")
answer = input("Is computer science your favourite subject? [Y/N] ")
agree = answer == "Y"
print("You're right; computer science is the best")

45. Develop
• Adapt this code by adding an else and ask a number of match
questions