Compilare: user.cpp: In function ‘int main()’: user.cpp:31: warning: comparison between signed and unsigned integer expressions user.cpp:35: warning: comparison between signed and unsigned integer expressions user.cpp:51: warning: comparison between signed and unsigned integer expressions user.cpp:56: warning: comparison between signed and unsigned integer expressions user.cpp:65: warning: comparison between signed and unsigned integer expressions user.cpp:76: warning: comparison between signed and unsigned integer expressions user.cpp:86: warning: comparison between signed and unsigned integer expressions