Loops (for & while)

A loop tells the computer 'do this again' without typing the same instruction over and over. Use a 'for' loop when you know how many times to repeat, like counting to 5. Use a 'while' loop when you want to keep going UNTIL something becomes true, like pouring water until the cup is full — however many pours that takes.

1. 1A `for` loop sets a counter, says how far to count, and says how much to add each time. It then repeats its body once per count.
2. 2A `while` loop checks a condition before every repeat. As long as it's true, the body runs again.
3. 3Every loop needs something that eventually stops it. The counter must run out, or the condition must become false. Otherwise the loop repeats forever.

Use a loop anytime you need to repeat an action. Use `for` when you know the number of times to repeat, and `while` when you repeat until a condition changes. Examples: going through every item in a list, retrying until something succeeds, or counting down to zero.

• ⚠Forgetting to change the thing the loop checks, like forgetting to lower the countdown. This makes the loop run forever — called an 'infinite loop'.
• ⚠Off-by-one mistakes. The loop runs one time too many or too few, because of how the start and end points are counted.