Compilare: main.cpp: In function 'void cifra()': main.cpp:61:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < numbers.size(); ++i) { ~~^~~~~~~~~~~~~~~~ main.cpp:63:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i < numbers.size() - 1) { ~~^~~~~~~~~~~~~~~~~~~~