# Loops that repeat Computers do not get bored. **Loops** repeat work. ## for loop ```python for i in range(5): print("Hello", i) ``` `range(5)` gives 0,1,2,3,4 — five times. ## while loop ```python n = 3 while n > 0: print(n) n = n - 1 ``` ## Danger A `while True:` with no `break` can run **forever**. That is an infinite loop. ## Why loops exist Printing the 1–10 table by hand is tiring. A loop does it in four lines — and never forgets 7 × 8. > If your program never stops, you probably forgot to change the loop variable. ## Loops are algebra’s sequences wearing running shoes The sequence 3, 6, 9, 12 is `3n` for n = 1, 2, 3, 4. In code: ``` for n in range(1, 5): print(3 * n) ``` Same table, automatic. ### Two loop families - **Counted** — you know how many times (for / repeat 10) - **Conditioned** — you know when to stop (while lives > 0) Both must be finite. Counted loops usually are. Conditioned loops need a change that will end the condition. ### When you are stuck Write the body once in English. Then say “repeat this for each …”. Then only wrap the loop.