Week 04 · Loop Logbooks
Thursday
Off by one
// Track a box through every lap
⏱ about 15 min
Count the laps carefully!
Rocket wanted the steps box to reach 5.
But his loop stopped at 4.
Rocket laughs. He counted one lap short!
Coders call this an off by one bug.
Even grown-up coders make this bug.
Raven says it is a great bug to hunt.
WARM-UP: THE BOX COUNTS LAPS
- Peek in the box.
- Tap how many laps.
set steps to 3
repeat steps times:
clap wings
?
set steps to 1
change steps by 1
repeat steps times:
flash lights
?
Four or five?
Rocket wants steps to reach 5.
But his loop runs only 4 laps.
Steps stops at 4. One short!
set steps to 0 repeat 4 times: change steps by 1 move right stop say steps
Off by one
Off by one means one too few.
Or it means one too many.
Count the laps to find it.
Start at the first number. Add 1 each lap.
| first line | loop line | ends on 5? |
|---|---|---|
| set steps to 0 | repeat 4 times: | ? |
| set steps to 0 | repeat 5 times: | ? |
| set steps to 1 | repeat 4 times: | ? |
| set steps to 1 | repeat 5 times: | ? |
WHERE DOES STEPS END?
- Count every lap.
- Tap the answer.
set steps to 1
repeat 4 times:
change steps by 1
?
set steps to 2
repeat 3 times:
change steps by 1
stop
say steps
?
set steps to 1
repeat 5 times:
change steps by 1
?
Fix the flight a new way.
Steps starts at 1 this time.
Nova must say 5.
BUILD A FLIGHT THAT ENDS ON 5
- Start at 1, loop 4 laps.
- Stop the loop, then say steps.
1line 1
2line 2
3line 3
4line 4
5line 5
The flight logbook
Look at the height column.
It stays at 3, then drops to 1.
The drop happens on lap 5.
Steps holds 5 right then!
Find the row where height changes.
| clue | true? |
|---|---|
| height drops on lap 5 | ? |
| steps holds 5 at the drop | ? |
| height drops on lap 2 | ? |
| height goes up at the drop | ? |
Off by one, fixed!
Off by one: one lap too few or many.
Count laps and check the start.
The drop came when steps held 5.
Great detective work, Crew!