Loops: Do It Again

Lesson 5 of 10 · 7 min · Free, no account needed

What you will learn

A for loop runs its indented body once for every value: each round is an iteration.
range(5) gives 0, 1, 2, 3, 4: it starts at 0 and stops before 5.
range(start, stop, step): range(2, 11, 2) gives 2, 4, 6, 8, 10.
Change one number and the loop does ten times the work.

Print the numbers from 1 to 100.
Would you type 100 lines? Tap to type them, one at a time.
Each step is one value of i. Where does i light up last?
Read the loop, then tap a step.
Run the loop and watch i climb.
Press Step. The body runs once for every step.
The parts of a loop have names.
A for loop repeats. The indented lines under it are the body.
Each round of the body is an iteration. The loop variable i holds a new value every round.
range(5) makes 0, 1, 2, 3, 4. range(1, 6) starts at 1 and stops before 6, so this loop prints 1 to 5. And range(1, 101) prints 1 to 100.
Make it print 2, 4, 6, 8, 10.
range can take a start, a stop and a step. Turn the three numbers.
Add up 1 to 5. Be the machine.
Every round, drag the new value of total into its box. Then press Check.
Pattern painter: paint the dashed stairs.
Up to 4 blocks in the loop. Set how many times it repeats. Paint exactly the pattern.
AI learns in a loop too. Build its training loop.
Put the stations in order. The last one sends it back for another round.
This should print 1 to 10. It stops at 9.
Tap the number that's off, fix it, then Run.
Your loop, ten times bigger.
Change how many times it repeats, then Run.

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