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6. Loops with Conditions (micro:bit)

Previously, we used loops like while True: that run forever.

However, we can add a condition to a loop so it stops when the condition is no longer true. This makes it similar to an if statement, but it repeats.

6.1 Example: Counter with a While Loop

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from microbit import *

count = 0
MAX_COUNT = 10

while count < MAX_COUNT:
    display.show(str(count))
    sleep(500)
    count = count + 1

display.clear()

What is happening?

• count starts at 0
• The loop runs while count is less than 10
• Each loop:
• Displays the number
• Waits 500ms
• Increases count by 1
• Stops when count reaches 10

Think About It

• How many times does this loop run?
• What changes if we use:

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while count <= MAX_COUNT:

6.2 Key Parts of a While Loop

To make a loop work correctly:

1. Tracking variable

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   count = 0

2. Condition

   1	while count < MAX_COUNT:

3. Update the variable

   1	count = count + 1

Common Mistakes

• If the variable never changes, the loop becomes infinite
• If the condition never becomes false, the loop never stops
• Incorrect update such as:

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count = count - 1

6.3 Practice: How Many Times?

How many times will each loop run?

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count = 0

while count < 20:
    print(count)
    sleep(200)
    count = count + 1

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count = 0

while count <= 20:
    print(count)
    sleep(200)
    count = count + 1

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count = 1

while count < 20:
    print(count)
    sleep(200)
    count = count + 1

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count = 0

while count == 20:
    print(count)
    sleep(200)
    count = count + 1

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count = 0

while count < 20:
    print(count)
    sleep(200)
    count = count + 2

7. For Loops (Better for Counters)

A for loop is often cleaner when you know how many times to repeat something.

7.1 Example: Using a For Loop

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from microbit import *

MAX_COUNT = 10

for count in range(MAX_COUNT):
    display.scroll(count)
    sleep(500)

display.clear()

7.2 Why For Loops are Easier

• No need to create count = 0
• No need to manually increase it
• Automatically runs the correct number of times

7.3 Understanding This Line

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for count in range(MAX_COUNT):

• for starts the loop
• count is the loop variable
• in is a required keyword
• range(MAX_COUNT) generates numbers from 0 to MAX_COUNT - 1

7.4 Key Idea

While loops are best when you do not know how long the loop will run.
For loops are best when you know the number of repetitions.