Compilare: main.cpp: In function 'void multiply()': main.cpp:44:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i <= n1.size() + n2.size();++i) ~~^~~~~~~~~~~~~~~~~~~~~~~~ main.cpp:47:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1;i <= n1.size();++i) ~~^~~~~~~~~~~~ main.cpp:48:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 1;j <= n2.size();++j) ~~^~~~~~~~~~~~