Compilare: user.cpp: In function ‘int main()’: user.cpp:31:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(a[x1].size()!=0 && y1<=a[x1].size()) ^ user.cpp:33:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(y2>=a[x2].size()) ^ user.cpp:37:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(y1==a[x1].size()-1) ^ user.cpp:46:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<a[i].size();j++) ^