Recently I came across one nice problem, which turned up as simple to understand as hard to find any way to solve. The problem is:
Write a program, that reads a text from input and prints some other program on output. If we compile and run the printed program, it must output the original text.
The input text is supposed to be rather large (more than 10000 characters).
The only (and very strong) requirement is that the size of the archive (i.e. the program printed) must be strictly less than the size of the original text. This makes impossible obvious solutions like
std::string s;
/* read the text into s */
std::cout << "#include<iostream> int main () { std::cout<<\"" << s << "\"; }";
I believe some archiving techniques are to be used here.