Note from former student - if C++ Bignum not installed == an alternative
  is (I cannot guarantee that this will always work!)

//  Project uses Integer.h/Integer.c Library and must
//  be compiled as follows:
//  g++ programname.C Integer.c -lgmp -lm

   Integer.h   
   Integer.c   

 LIP  
tarred and zipped version of lip a LIP makefile 

BigNum 
 Documentation on Bignum -  compiling with the Integer Class bignum.h"
       C and assember source code for bignumexample of Bignum program 


 MIRACL a free large integer package: note 


 Others 
info on gmp (C) GNU's multiprecisio lib.
Large Integer  for VB, XBasic, Free Basic list of C packages  note date of list
a tour of NTL downloads of UBasic Jeff Walton's Big Num for Visual Basic