Compilare: user.cpp: In function 'void df(int)': user.cpp:56: warning: unused variable 'y' user.cpp: In function 'int main()': user.cpp:129: warning: unused variable 'z' user.cpp:146: warning: 'a' may be used uninitialized in this function user.cpp:146: warning: 'b' may be used uninitialized in this function