Compilare: user.cpp: In function ‘void make_prefix()’: user.cpp:15:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=2; i<a.length(); ++i){ ^ user.cpp: In function ‘int main()’: user.cpp:42:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=1; i<b.length(); ++i) { ^ user.cpp:48:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k==a.length()) { ^ user.cpp:58:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i<sol.size(); ++i) cout<<sol[i]<<" "; ^