You are right about it starting on 41, but chances are that that is its intended behavior, with a bit of context that is more clear:

  #define ARRAYSIZE 42

  int array[ARRAYSIZE];

  void f() {
     for (i=ARRAYSIZE; i --> 0;) {
       printf("%d\n", array[i]);
     }
  }

If it were to start at 42 you'd be referencing the array outside of its bounds.

In C you're used to less-than-one loops though. for(i = 0; i < 5; i++) terminates on 4. And it's what you want if you're going through an array.