Compilare: main.cpp: In function 'void rec(int, int)': main.cpp:16:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (j < matrix[x][y].size()) ~~^~~~~~~~~~~~~~~~~~~~~ main.cpp:24:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j >= matrix[x][y].size()) ~~^~~~~~~~~~~~~~~~~~~~~~