Compilare: user.cpp: In function ‘void df(int)’: user.cpp:15: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void back_df(int)’: user.cpp:24: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void comp_df(int)’: user.cpp:31: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:61: warning: comparison between signed and unsigned integer expressions user.cpp:75: warning: comparison between signed and unsigned integer expressions user.cpp:78: warning: comparison between signed and unsigned integer expressions