Compilare: user.cpp: In function ‘void split_tokens(std::string&)’: user.cpp:13:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (end = 1; end < line.size(); ++end) { ^ user.cpp: In function ‘void solve(std::string, std::ofstream&)’: user.cpp:30:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < tokens.size(); ++i) { ^ user.cpp:39:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < tokens.size(); ++i) { ^