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    <blockquote> <p>So am I right in saying that if n=11111, 5 sum variables are created and pushed on the stack with each recursion?</p> </blockquote> <p>Conceptually, but compilers may turn some forms of recursion into jumps/loops. E.g. a compiler that does tail call optimization may turn</p> <pre><code>void rec(int i) { if (i &gt; 0) { printf("Hello, level %d!\n", i); rec(i - 1); } } </code></pre> <p>into the equivalent of</p> <pre><code>void loop(int i) { for (; i &gt; 0; i--) printf("Hello, level %d!\n", i); } </code></pre> <p>because the recursive call is in <em>tail position</em>: when the call is made, the current invocation of <code>rec</code> has no more work to do except a <code>return</code> to its caller, so it might as well reuse its stack frame for the next recursive call.</p> <blockquote> <p>If this is correct then what is the benefit of using recursion when I can do it in normal function using loops, thus overwriting only one memory location? If I use pointers, recursion will probably take similar memory as a normal function.</p> </blockquote> <p>For this problem, recursion is a pretty bad fit, at least in C, because a loop is much more readable. There are problems, however, where recursion is easier to understand. Algorithms on tree structures are the prime example.</p> <p>(Although every recursion can be emulated by a loop with an explicit stack, and then stack overflows can be more easily caught and handled.)</p> <p>I don't understand the remark about pointers.</p> <blockquote> <p>I don't see how the recursions (other than the last one which returns 0) return values without uncommenting line 3.</p> </blockquote> <p>By chance. The program exhibits undefined behavior, so it may do anything, even return the correct answer.</p>
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    1. COThanks for explaining the concept of tail call optimization. When I said about using pointers, I wasn't really referring to any particular problem but was implying that we could change the value at a memory location in a hypothetical problem without creating unnecessary variables but I guess compiler would most probably optimize any recursion where a variable goes unused after an instance.
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    2. CO@aste123: in "true" (unoptimized) recursion, you'd still need a pointer per recursive invocation :)
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