Iteration in C

Hi there /prog/.

I know Python, and I'm learning C. Both langs have for loops. Python's nicely iterates over a collection of unknown length. C's usually has you specify the length of the collection at compile time, but what if the length is unknown?

My best newbie guess: you terminate the collection with NULL, or you write an iteration function that returns some end-of-collection value when it's done.

>>1,4,7,9,12
Or you store the length separately you goddamn fucking retards.

struct Foo {
  struct Bar* bars;
  int bars_count;
};