GNU g++ header file.

/********************************************************
* #include <_string>
* #include <_iostream> //this is a very commonly used one.
* #include <_fstream> // commonly used.
* #include <_iomanip> //commonly used.
* #include <_vector>
* #include "nr.h"
*********************************************************/
Note, in the program, there should not have '_' before string, or others. Here it is
used to display the content.