Compilare: user.cpp: In function ‘int main()’: user.cpp:20: warning: comparison between signed and unsigned integer expressions user.cpp:24: warning: comparison between signed and unsigned integer expressions user.cpp:27: warning: comparison between signed and unsigned integer expressions user.cpp:31: warning: comparison between signed and unsigned integer expressions user.cpp:43: warning: comparison between signed and unsigned integer expressions user.cpp:47: warning: comparison between signed and unsigned integer expressions user.cpp:52: warning: comparison between signed and unsigned integer expressions