Is this a loop?

Question

Is this a loop, not a loop, or both a loop and not a loop? If you're counting the number of loops in a program, would you count this?

do {
   ...
}while(0);

I'm curious because I'm working with someone who has a project that requires him to count the number of loops in a program.

It's a while loop, despite the false value, so I assume it is. — Jeremy, Jul 14 '16 at 14:07
It's as much a loop as `for (int i = 0; i < 1; i++) { /* ... */ }` — pmg, Jul 14 '16 at 14:09
@DombiSzabolcs: Seriously? What ever happened to just [trying it out yourself](http://ideone.com/RhGHca) before posting? — Kerrek SB, Jul 14 '16 at 14:16
The compiler might completly optimize away the `while` construct, so all that would be left in the compiled binary is the `...` part. — Jabberwocky, Jul 14 '16 at 14:16
BTW why would you need to know the number of loops in your program ? — Jabberwocky, Jul 14 '16 at 14:18
@MichaelWalz - `re: "why would you need to know...."`, homework, for sure — KevinDTimm, Jul 14 '16 at 14:29
You are effectively asking for a definition of "loop". To the extent that there is any uncertainty or room for disagreement, this is a matter of opinion, and thus not appropriate for an SO question. — John Bollinger, Jul 14 '16 at 14:30
I don't see the point in counting the number of loops, a better approach IMHO would be counting the time complexities of the loops. This one in particular has O(1). — babon, Jul 14 '16 at 15:09
This question does not ask about the usage of `do...while..`, as was in the marked dupes. As I already commented, IMHO, this is not a dupe, please let me know if anyone disagrees. — Sourav Ghosh, Jul 15 '16 at 07:11

score 7 · Accepted Answer · edited Jun 20 '20 at 09:12

In C standard, C11, chapter §6.8.5, Iteration statements, it is listed

iteration-statement:

       while ( expression ) statement
       do statement while ( expression ) ;
       for ( expression _opt ; expression _opt ; expression _opt ) statement
       for ( declaration expression _opt ; expression _opt ) statement

The do statement while ( expression ) ; is mentioned, so yes, it is a loop (iteration) statement, irrespective of the number of iterations it make in a particular implementation/usage.

FWIW, this loops one time.

To add some more clarification, quoting from Wikipedia, (emphasis mine)

A loop is a sequence of statements which is specified once but which may be carried out several times in succession. The code "inside" the loop (the body of the loop, shown below as xxx) is obeyed a specified number of times, or once for each of a collection of items, or until some condition is met, or indefinitely.

@vjb words can be tricky. this is obviously a _loop statement_ with an iteration of _exactly_ one time. — Sourav Ghosh, Jul 14 '16 at 14:24

score 2 · Answer 2 · edited May 23 '17 at 10:30

2

In a sense, yes it is a loop, but in reality no. It is technically a loop because you are using loop syntax, but what you're actually doing is just running the code in your "loop" once, and then breaking. I wouldn't really count it as a loop because you're not adding any algorithmic runtime to your program, so there's no point in counting it as a loop. Note: don't do this, it is pointless and bad coding practice.

EDIT: Credits to Jeremy in the comments below, there is at least one case where this construct can be useful in C: do { ... } while (0) — what is it good for?

edited May 23 '17 at 10:30

Community

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answered Jul 14 '16 at 14:08

Andrew

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It's also an enormously widespread construct used in almost every macro. – Kerrek SB Jul 14 '16 at 14:09
@KerrekSB At least, one would hope so. In reality, many macros are made without this… – glglgl Jul 14 '16 at 14:09
http://stackoverflow.com/questions/257418/do-while-0-what-is-it-good-for – Jeremy Jul 14 '16 at 14:11
unless of course some condition internally 'runs' a `continue' and then you run more than once – KevinDTimm Jul 14 '16 at 14:31
@KevinDTimm: Can you make an example and link to it? – Kerrek SB Jul 14 '16 at 15:06
@KerrekSB - can't figure out where to store an example but `do { ....; i = getVar(); if (i < 0) continue; .....; } while (0);` – KevinDTimm Jul 14 '16 at 16:17
@KevinDTimm: I don't understand at which part of your code you "run more than once". – Kerrek SB Jul 14 '16 at 17:01
@KerrekSB - you are correct, I forgot that `continue` does not go to the top of the loop but instead goes to the control statement - Mea Culpa and thanks for the reminder :) – KevinDTimm Jul 14 '16 at 17:07

score 0 · Answer 3 · answered Jul 14 '16 at 14:10

0

do {
   ...
}while(k);

Now the number of iterations depend on the value of k, now you cant say something like its a loop only if k!=0 or if k is True.

So its basically a loop.

answered Jul 14 '16 at 14:10

shiva

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Is this a loop?

3 Answers3