Compilare: In file included from /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward/fstream.h:31, from user.cpp:1: /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples include substituting the <X> header for the <X.h> header for C++ includes, or <iostream> instead of the deprecated header <iostream.h>. To disable this warning use -Wno-deprecated. user.cpp:56:2: warning: no newline at end of file user.cpp: In function 'int valid(int)': user.cpp:9: warning: unused variable 'd' user.cpp: In function 'void back()': user.cpp:37: warning: statement has no effect user.cpp: In function 'int main()': user.cpp:51: warning: converting to non-pointer type 'char' from NULL user.cpp: In function 'int valid(int)': user.cpp:16: warning: control reaches end of non-void function