Compilare: user.cpp: In function ‘std::string intersect(std::string, std::string)’: user.cpp:16:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < A.size(); ++i) ^ user.cpp: In function ‘int solve(std::string)’: user.cpp:29:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < X.size(); ++i) ^ user.cpp:39:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < X.size(); ++i) ^ user.cpp:40:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i != X.size() / 2) ^ user.cpp:48:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < X.size(); ++i) ^ user.cpp:49:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i != X.size() / 2) ^ user.cpp:51:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < X.size() / 2; ++i) ^ user.cpp:53:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = X.size() / 2; i < X.size(); ++i) ^ /tmp/ccqjZO9W.o: In function `main': user.cpp:(.text.startup+0xe0): warning: the `gets' function is dangerous and should not be used.