Compilare: user.cpp: In function ‘void add(hkey&)’: user.cpp:22: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void read()’: user.cpp:35: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:37: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:43: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void solve()’: user.cpp:61: warning: comparison between signed and unsigned integer expressions