Compilare: user.cpp: In function ‘int mex(std::vector<int>)’: user.cpp:10:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(auto x : v) if(app.size() > x) app[x] = true; ~~~~~~~~~~~^~~ user.cpp:11:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < v.size(); ++i) ~~^~~~~~~~~~ user.cpp:13:23: warning: control reaches end of non-void function [-Wreturn-type] return i; } ^