Compilare: main.cpp: In constructor 'Matrix::Matrix(std::vector<std::vector<int> >)': main.cpp:25:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); ++i){ ~~^~~~~~~~~~ main.cpp:27:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < a[i].size(); ++j){ ~~^~~~~~~~~~~~~ main.cpp: In member function 'Matrix Matrix::operator*(const Matrix&)': main.cpp:34:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); ++i){ ~~^~~~~~~~~~ main.cpp:37:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); ++i){ ~~^~~~~~~~~~ main.cpp:38:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < b.a[0].size(); ++j){ ~~^~~~~~~~~~~~~~~ main.cpp:39:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < b.a.size(); ++k){ ~~^~~~~~~~~~~~