Compilare: user.cpp: In function ‘void out_a()’: user.cpp:29:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<b.size(); ++i) ^ user.cpp: In function ‘void out_b()’: user.cpp:48:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<b.size(); ++i) ^ user.cpp: In function ‘void gen_b()’: user.cpp:57:9: warning: unused variable ‘i’ [-Wunused-variable] int i=n; ^