Compilare: user.cpp: In function 'bool check(int)': user.cpp:10: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'void back(int, int, double)': user.cpp:20: warning: comparison between signed and unsigned integer expressions user.cpp:22: warning: comparison between signed and unsigned integer expressions user.cpp:25: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:56: warning: unused variable 'r' user.cpp:33: warning: unused variable 'y' user.cpp:33: warning: unused variable 'z'