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POGuideline: while vs for
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copied!<p><em>Disclaimer: I tried to search for similar question, however this returned about every C++ question... Also I would be grateful to anyone that could suggest a better title.</em></p> <p>There are two eminent loop structure in C++: <code>while</code> and <code>for</code>.</p> <ul> <li>I purposefully ignore the <code>do ... while</code> construct, it is kind of unparalleled</li> <li>I know of <code>std::for_each</code> and <code>BOOST_FOREACH</code>, but not every loop is a <code>for each</code></li> </ul> <p>Now, I may be a bit tight, but it always itches me to <em>correct</em> code like this:</p> <pre><code>int i = 0; while ( i < 5) { // do stuff ++i; // I'm kind and use prefix notation... though I usually witness postfix } </code></pre> <p>And transform it in:</p> <pre><code>for (int i = 0; i < 5; ++i) { // do stuff } </code></pre> <p>The advantages of <code>for</code> in this example are multiple, in my opinion:</p> <ol> <li><strong>Locality</strong>: the variable i only lives in the scope of the loop</li> <li><strong>Pack</strong>: the loop 'control' is packed, so with only looking at the loop declaration I can figure if it is correctly formed (and will terminate...), assuming of course that the loop variable is not further modified within the body</li> <li>It may be inlined, though I would not always advised it (that makes for tricky bugs)</li> </ol> <p>I have a tendency therefore not to use <code>while</code>, except perhaps for the <code>while(true)</code> idiom but that's not something I have used in a while (pun intended). Even for complicated conditions I tend to stick to a <code>for</code> construct, though on multiple lines:</p> <pre><code>// I am also a fan of typedefs for (const_iterator it = myVector.begin(), end = myVector.end(); it != end && isValid(*it); ++it) { /* do stuff */ } </code></pre> <p>You could do this with a <code>while</code>, of course, but then (1) and (2) would not be verified.</p> <p>I would like to avoid 'subjective' remarks (of the kind "I like for/while better") and I am definitely interested to references to existing coding guidelines / coding standards.</p> <p><strong>EDIT</strong>: </p> <p>I tend to really stick to (1) and (2) as far as possible, (1) because locality is recommended >> <a href="http://www.gotw.ca/publications/c++cs.htm" rel="nofollow noreferrer">C++ Coding Standards: Item 18</a>, and (2) because it makes maintenance easier if I don't have to scan a whole body loop to look for possible alterations of the control variable (which I takes for granted using a <code>for</code> when the 3rd expression references the loop variables).</p> <p>However, as <code>gf</code> showed below, while do have its use:</p> <pre><code>while (obj.advance()) {} </code></pre> <p>Note that this is not a rant against <code>while</code> but rather an attempt to find which one of <code>while</code> or <code>for</code> use depending on the case at hand (and for sound reasons, not merely liking).</p>

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