Compilare: user.cpp: In function ‘int main()’: user.cpp:36:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<b.size();i++) out<<b.at(i)<<" "; ^ user.cpp:15:22: warning: unused variable ‘N’ [-Wunused-variable] int M=m.length(),N=n.length(),i=M,j=M,a=0; ^