Compilare: user.cpp: In function ‘void hull()’: user.cpp:29:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=1;i<down.size();i++) ^ user.cpp: In function ‘int main()’: user.cpp:7:11: warning: unused variable ‘first’ [-Wunused-variable] #define x first ^ user.cpp:39:11: note: in expansion of macro ‘x’ int i,x,y; ^ user.cpp:8:11: warning: unused variable ‘second’ [-Wunused-variable] #define y second ^ user.cpp:39:13: note: in expansion of macro ‘y’ int i,x,y; ^