Compilare: user.cpp: In function ‘void read()’: user.cpp:19:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.size(); i++) ^ user.cpp: In function ‘void magic(std::vector<std::vector<int> >&)’: user.cpp:34:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.size(); i++) ^ user.cpp: In function ‘void solve()’: user.cpp:51:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1; i<x.size(); i++) ^ user.cpp:52:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=i+1; j<x.size(); j++) ^ user.cpp: At global scope: user.cpp:62:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^