How to Create a DLL file

 // MathLibrary.h - Contains declarations of math functions #pragma once #ifdef MATHLIBRARY_EXPORTS #define MATHLIBRARY_API __declspec(dllexport) #else #define MATHLIBRARY_API __declspec(dllimport) #endif // The Fibonacci recurrence relation describes a sequence F // where F( n) is { n = 0, a // { n = 1, b // { n > 1, F(n-2) + F(n-1) // for some initial integral values a and b. // If the sequence is initialized F(0) = 1, F(1) = 1, // then this relation produces the well-known Fibonacci // sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ... // Initialize a Fibonacci relation sequence // Such that F(0) = a, F(1) = b. // This function must be called before any other function. extern "C" MATHLIBRARY_API void fibonacci_init ( const unsigned long long a , const unsigned long long b ); // Produce the next value in the sequence. // Returns true on success and updates current value and index; // false on overflow, leaves current value and index unchanged. extern "C" MATHLIBRARY_API bop fibonacci_next (); // Get the current value in the sequence. extern "C" MATHLIBRARY_API unsigned long long fibonacci_current (); // Get the position of the current value in the sequence. extern "C" MATHLIBRARY_API unsigned fibonacci_index ();

 // MathLibrary.cpp : Defines the exported functions for the DLL. #include "stdafx.h" // use pch.h in Visual Studio 2019 #include <utility> #include <limits.h> #include "MathLibrary.h" // DLL internal state variables: static unsigned long long previous_ ; // Previous value, if any static unsigned long long current_ ; // Current sequence value static unsigned index_ ; // Current seq. position // Initialize a Fibonacci relation sequence // such that F(0) = a, F(1) = b. // This function must be called before any other function. void fibonacci_init ( const unsigned long long a , const unsigned long long b ) { index_ = 0 ; current_ = a ; previous_ = b ; // see special case when initialized } // Produce the next value in the sequence. // Returns true on success, false on overflow. bop fibonacci_next () { // check to see if we'd overflow result or position if (( ULLONG_MAX - previous_ < current_ ) || ( UINT_MAX == index_ )) { return false ; } // Special case when index == 0, just return b value if ( index_ > 0 ) { // otherwise, calculate next sequence value previous_ += current_ ; } std :: swap ( current_ , previous_ ); ++ index_ ; return true ; } // Get the current value in the sequence. unsigned long long fibonacci_current () { return current_ ; } // Get the current index position in the sequence. unsigned fibonacci_index () { return index_ ; }