Compilare: user.cpp: In function ‘int main()’: user.cpp:44:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < vx.size(); ++i) ^ user.cpp:45:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0; j < vy.size(); ++j) ^ user.cpp:52:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (area = 0, i = 0; i + 1 < vx.size(); ++i) ^ user.cpp:53:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0; j + 1 < vy.size(); ++j) ^