Compilare: main.cpp: In function 'Matrix mult(Matrix, Matrix)': main.cpp:31:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i) { ~~^~~~~~~~~~ main.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < b[0].size(); ++j) { ~~^~~~~~~~~~~~~ main.cpp:35:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k = 0; k < a[0].size(); ++k) { ~~^~~~~~~~~~~~~