Compilare: user.cpp: In function ‘void get_prefix()’: user.cpp:24: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void print_prefix()’: user.cpp:52: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void find_matches()’: user.cpp:59: warning: comparison between signed and unsigned integer expressions user.cpp:65: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void write()’: user.cpp:101: warning: comparison between signed and unsigned integer expressions