4 ms·

I wonder if I'm alone in thinking that the original `while` version is easier to read and understand than the ending `for` version. I've never quite understood

I wonder if I'm alone in thinking that the original `while` version is easier to read and understand than the ending `for` version. I've never quite understood C programmers' love of the `for` loop. It's just a `while` loop with the different parts stuck in different places (`init; while (cond) { ...; inc; }` is the same as `for(init; cond; inc) { ...; }`) and it doesn't (at least for me) result in any greater clarity or ease in reasoning.

RiderOfGiraffes 16y ago
Actually, they are not the same. See the trivia question in the lunk article.
- jemfinch 16y ago
  I saw the trivia question in the link article, but it doesn't provide an answer, so I ignored it. EDIT: K&R says (page 60 in my second edition): """ The for statement for (expr1; expr2; expr3) statement is equivalent to expr1; while (expr2) { statement expr3; } except for the behavior of continue, which is described in Section 3.7. """ So apparently the trivia is the behavior of `continue`, which I think most C programmers (including myself) would know implicitly, even if we couldn't answer the question itself.
  - RiderOfGiraffes 16y ago
    And it's because the knowledge is implicit and used when appropriate without thinking about it, that the question is, in my opinion, pointless as an interview question, except perhaps to see how the candidate reacts to it.
edanm 16y ago
I think for loops are better than while loops for looping over arrays. I'll try and explain my reasoning: Whenever you see a `for` loop, it tells you something that a `while` loop doesn't. It tells you the kind of loop you're about to do. A `for` (usually) means you're going to be looping over an array, with a specific length, with a specific "step" (usually one). This is information you immediately get by seeing a `for`. Moreover, you get all the information about how the loop looks (what you're looping over, size of the array, other actions you intend to perform in the loop) all in one place. This especially helps when you're looking at a large piece of code, in which case your example of "while (cond) {...;inc;}" would have a lot of lines between the condition and the increment.
- RiderOfGiraffes 16y ago
  But I observe that in C when iterating over a string you don't know in advance how big it is, you merely have to keep going until you find the '\0'. That's why some people will find it more natural to use a "while" when walking down a string.
- jemfinch 16y ago
  > I think for loops are better than while loops for looping over arrays. I'll try and explain my reasoning: > Whenever you see a `for` loop, it tells you something that a `while` loop doesn't. It tells you the kind of loop you're about to do. I won't disagree with that in theory, but I don't really think the "for" loop is the solution. The real solution, I think, is a "foreach" construct (whether it's a loop built into the language (á la Java/C#) or a higher-order function (á la C++'s std::for_each), I don't really care) for iterating over arrays and other collections. In practice, I think the for loop is too often abused for too little gain, and I think C would be a better language without it. As an aside, I wonder if anyone has provided a suitable Hoare triple for C's for loop. I have an idea of what it would look like, but would love to see someone else's efforts to verify my own internalized one.
  - edanm 16y ago
    I love higher language's foreach construct. Have to work with what we've got though, and in C, the `for` loop is it. By the way, I don't know what a Hoare triple is, and reading a little on Wikipedia didn't enlighten me. Any chance for an explanation?
    - jemfinch 16y ago
      I assume you read http://en.wikipedia.org/wiki/Hoare_logic http://en.wikipedia.org/wiki/Hoare_logic ? Basically, the (relevant) state of the computation is represented as a set of logical propositions which are true before a statement, and a set of logical propositions which are true after the statement. For each kind of statement the language supports (`if` statements, `while` statements, etc.) there are natural ways to reason about those triples. Do you understand the "While rule" on the link above? I can explain it in natural language, but I'd rather not expend the effort if it's not something you've already seen.

RiderOfGiraffes 16y ago

Actually, they are not the same. See the trivia question in the lunk article.

jemfinch 16y ago
I saw the trivia question in the link article, but it doesn't provide an answer, so I ignored it. EDIT: K&R says (page 60 in my second edition): """ The for statement for (expr1; expr2; expr3) statement is equivalent to expr1; while (expr2) { statement expr3; } except for the behavior of continue, which is described in Section 3.7. """ So apparently the trivia is the behavior of `continue`, which I think most C programmers (including myself) would know implicitly, even if we couldn't answer the question itself.
- RiderOfGiraffes 16y ago
  And it's because the knowledge is implicit and used when appropriate without thinking about it, that the question is, in my opinion, pointless as an interview question, except perhaps to see how the candidate reacts to it.

edanm 16y ago

I think for loops are better than while loops for looping over arrays. I'll try and explain my reasoning: Whenever you see a `for` loop, it tells you something that a `while` loop doesn't. It tells you the kind of loop you're about to do. A `for` (usually) means you're going to be looping over an array, with a specific length, with a specific "step" (usually one). This is information you immediately get by seeing a `for`. Moreover, you get all the information about how the loop looks (what you're looping over, size of the array, other actions you intend to perform in the loop) all in one place. This especially helps when you're looking at a large piece of code, in which case your example of "while (cond) {...;inc;}" would have a lot of lines between the condition and the increment.

RiderOfGiraffes 16y ago
But I observe that in C when iterating over a string you don't know in advance how big it is, you merely have to keep going until you find the '\0'. That's why some people will find it more natural to use a "while" when walking down a string.
jemfinch 16y ago
> I think for loops are better than while loops for looping over arrays. I'll try and explain my reasoning: > Whenever you see a `for` loop, it tells you something that a `while` loop doesn't. It tells you the kind of loop you're about to do. I won't disagree with that in theory, but I don't really think the "for" loop is the solution. The real solution, I think, is a "foreach" construct (whether it's a loop built into the language (á la Java/C#) or a higher-order function (á la C++'s std::for_each), I don't really care) for iterating over arrays and other collections. In practice, I think the for loop is too often abused for too little gain, and I think C would be a better language without it. As an aside, I wonder if anyone has provided a suitable Hoare triple for C's for loop. I have an idea of what it would look like, but would love to see someone else's efforts to verify my own internalized one.
- edanm 16y ago
  I love higher language's foreach construct. Have to work with what we've got though, and in C, the `for` loop is it. By the way, I don't know what a Hoare triple is, and reading a little on Wikipedia didn't enlighten me. Any chance for an explanation?
  - jemfinch 16y ago
    I assume you read http://en.wikipedia.org/wiki/Hoare_logic http://en.wikipedia.org/wiki/Hoare_logic ? Basically, the (relevant) state of the computation is represented as a set of logical propositions which are true before a statement, and a set of logical propositions which are true after the statement. For each kind of statement the language supports (`if` statements, `while` statements, etc.) there are natural ways to reason about those triples. Do you understand the "While rule" on the link above? I can explain it in natural language, but I'd rather not expend the effort if it's not something you've already seen.