If then with multiple expressions OCaml

How can I code, in OCaml, something like this (main() in C)

for (i=0; i<y; i++)
    if (x==5)
    {
        y=i;
        return true;
    }

It would return the boolean True and y would be equal to the corresponding i value.

Basically, in OCaml, I was wondering if you could have a if like:

for i=0 to y-1 do
        if x=5 then
        begin 
            y=i
            true
        end
        else ()
done;;

I know the lines between begin-end aren't correctly implemented. I don't even know if what I want to do is possible in OCaml. If you are someone who has knowledge on this kindly share it with me. Thanks!