Compilare: main.cpp: In function 'int main()': main.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int x = 0; x < b[i].size(); x++) ~~^~~~~~~~~~~~~ main.cpp:36:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int y = x; y < b[i].size(); y++) ~~^~~~~~~~~~~~~ main.cpp:46:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int x = 0; x < a[i].size(); x++) ~~^~~~~~~~~~~~~ main.cpp:49:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int y = x; y < a[i].size(); y++) ~~^~~~~~~~~~~~~