1
$\begingroup$

I came across this hoare logic for factorials but I don't quite understand it. We multiply F and X but we're not adding up all values of F so how do we get the sum/factorial at the end?

Precondition: $\{ X > 0 \land X = x \}$

  1. $F := 1$
  2. while $X > 0$ do
  3. $\quad F := F \cdot X$
  4. $\quad X := X - 1$
  5. od

Postcondition: $\{F = x!\}$

$\endgroup$
  • $\begingroup$ I don't see any sum at the end. $\endgroup$ – Yuval Filmus Apr 5 at 16:06
0
$\begingroup$

What the Hoare invariant state is the following:

If you run the code with $X$ equal to some value $x > 0$, then at the end, $F$ will have the value $x!$ ($x$ factorial).

You can check that this is indeed the case.

| cite | improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.