14. EXT: for-loops

14.1. Using if to test strings within for-loops

What does this code do?

name[0] in "AEIOU" returns True if the first character in the name string is in hte string of vowels.

A string can be changed to upper case using .upper().

e.g. anna.upper() returns “ANNA”

The code below scrolls the name in upper case only if the first letter is a vowel.

from microbit import *

name = "Anna"
while True:
    if name[0] in "AEIOU":
        display.scroll(name.upper(), delay=50)

Tasks

Write a for-loop to scroll names beginning with a vowel in [‘Olivia’, ‘Emily’, ‘Chloe’, ‘Catherine’, ‘Anna’, ‘Gabriella’, ‘Hannah’, ‘Isabel’, ‘Julia’]. Display the names in uppercase.

14.2. for-loops with mixed lists

Mixed lists can be used with display.show.
Strings, integers and floats, and Images can all be displayed with display.show.
A short delay is used in display.show for when there are multipel characters in a string or number.
A short sleep is used in the for-loop so that there is a noticable gap betwwen each list element no matter whether they are strings, numbers or images.
A longer sleep is used after the for-loop before it repeats.

from microbit import *

mixed_list = ['I', Image.HEART, 3.14]
while True:
    for element in mixed_list:
        display.show(element, delay=200)
        sleep(700)
    sleep(1000)

Tasks

Create a mixed list to display the message to be asleep at 10 o’clock.
Create a mixed list to display you’re 3 favourite animals with their number order.

14.3. Nested for-loops

A loop within another loop within is called a nested loop.

The code below loops through each list and displays the result of joining each string.

from microbit import *

col_letters = ['A', 'B', 'C']
row_nums = ['1', '2', '3', '4']
while True:
    for col in col_letters:
        for row in row_nums:
            display.scroll(col + row, delay=200)

for col in col_letters takes each element in the list col_letters and puts it in the variable col for use in the loop.
for row in row_nums takes each element in the list row_nums and puts it in the variable row for use in the loop.
Each time the outer loop, for col in col_letters, runs 3 times since there are 3 elements in ['A', 'B', 'C'].
Each time the outer loop is run, the inner loop, for row in row_nums, runs 4 times since there are 4 elements in ['1', '2', '3', '4'].
The nested loops run a total of 3 * 4 or 12 times.
The + in col + row does a text join. When col = ‘A’ and row = ‘1’, col + row will result in 'A1'.

The nested loops below perform multiplication tables for 7 and 9.

The nested loops run a total of 2 * 9 or 18 times.

from microbit import *

nums_1_list = [7, 9]
nums_2_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
while True:
    for num_1 in nums_1_list:
        for num_2 in nums_2_list:
            display.scroll(num_1 * num_2, delay=80)

Tasks

Write a nested for-loop that finds the sum of every different combination of one number from each of the two lists: [1, 2, 3] and [6, 5, 4].
Write a nested for-loop that scrolls the 2 digit number formed from the joining of every different combination of one number from each of the two lists: [1, 2, 3] and [4, 5], keeping the digit from the first list first.