Standard C/C++: fetch the files lib.cpp and lib.h. You can make a directory where you store
these files, and eventually its compiled version lib.o. The example here is program1.cpp from chapter 6 and performs the matrix inversion.
// Simple matrix inversion example
#include <iostream>
#include <new>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include "lib.h"
using namespace std;
/* function declarations */
void inverse(double **, int);