Compilare: user.cpp: In function ‘void read()’: user.cpp:17:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp:21:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < a.size(); j++) ^ user.cpp: In function ‘void solve()’: user.cpp:28:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp:29:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < a.size(); j++) ^ user.cpp:30:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < a.size(); k++) ^ user.cpp: In function ‘void write()’: user.cpp:37:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++, cout << '\n') ^ user.cpp:38:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < a.size(); j++) ^