Compilare: user.cpp: In function ‘int main()’: user.cpp:116:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<u.size(); i++) ^ user.cpp:117:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0; j<u[i].size(); j++) ^ user.cpp:118:15: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(u[i][j]!=v[i][j]) ^