Compilare: user.cpp: In function ‘void read()’: user.cpp:18:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.size(); i++) ^ user.cpp: In function ‘int solve()’: user.cpp:28:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (a[i].size() < k) { ^ user.cpp: At global scope: user.cpp:36:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^