Loops

Enemy 1 of 5

for loops and Printf.printf

Writing the same instruction a dozen times by hand doesn't scale — if you needed to print every number from 1 to 1000, you'd want a way to describe "do this once per number" and let the language handle the repetition. OCaml's `for` loop does exactly that over a range of integers.

`for i = start to finish do ... done` counts from `start` to `finish`, **inclusive of both ends**, binding each value to `i` in turn. This is a genuine difference from many other languages' `for`/range constructs that exclude the upper bound — in OCaml, `for i = 0 to 2 do ... done` runs for `i = 0`, `1`, and `2`, three iterations total, both endpoints included. Keep this in mind, since assuming the upper bound is excluded (as it often is elsewhere) is an easy off-by-one mistake to make here.

`Printf.printf` is OCaml's formatted-printing function, modeled closely on C's `printf`: `"%d\n"` is a format string where `%d` is a placeholder for an integer argument and `\n` is an explicit newline character. `Printf.printf "%d\n" i` substitutes `i` into the `%d` slot and prints the result. This is a different, more general tool than `print_int`/`print_endline`, useful once you need to interleave multiple values and literal text in one line.