A loop repeats a block of code several times without rewriting it. It is essential for going through a list or counting.

The for loop

Ideal when you know how many repetitions you need. It has three parts: an initialisation, a condition and an increment.

• for ($i = 1; $i <= 5; $i++) repeats 5 times.
• $i++ increases $i by 1 on each pass.

The while loop

Ideal when you do not know the number of passes in advance: it keeps going as long as the condition stays true.

1. The condition is checked.
2. If it is true, the block runs.
3. It starts again until the condition becomes false.

Careful: always make sure the condition can change, otherwise the loop runs forever and freezes the script!

Key point: use for when you know the number of passes, and while when you loop « as long as » a condition is true.