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Heres a good puzzle: how do you write a program which produces its own source code as output?

April 26, 2017good output produces program puzzle source code write

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Heres a good puzzle: how do you write a program which produces its own source code as output?

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It is actually quite difficult to write a self-reproducing program that is truly portable, due particularly to quoting and character set difficulties. Here is a classic example (which ought to be presented on one line, although it will fix itself the first time it’s run): char*s=”char*s=%c%s%c;main(){printf(s,34,s,34);}”; main(){printf(s,34,s,34);} (This program has a few deficiencies, among other things neglecting to #include , and assuming that the double-quote character ” has the value 34, as it does in ASCII.) Here is an improved version, posted by James Hu: #define q(k)main(){return!puts(#k”\nq(“#k”)”);} q(#define q(k)main(){return!puts(#k”\nq(“#k”)”);}) comp.lang.c FAQ list · Question 20.35 Q: What is “Duff’s Device”? A: It’s a devastatingly devious way of unrolling a loop, devised by Tom Duff while he was at Lucasfilm. In its “classic” form, it was used to copy bytes, and looked like this: register n = (count + 7) / 8; /* count > 0 assumed */ switch (count % 8) { ca