Создание DLL

 #include <windows.h>
 #include "dll.h"
 int WINAPI DllMain(HINSTANCE hInstance, DWORD fdReason, PVOID pvReserved)
    {
        return TRUE;
    }
 
EXPORT int Random(int min, int max) 
{
    return min + rand() % (max - min);
}
 
EXPORT HBRUSH GenerateColor()
{
    return CreateSolidBrush(RGB(Random(0, 256), (0, 256), (0, 256)));
}
 
EXPORT void PaintFigure(HWND hWnd, int code, int x, int y, LPARAM lParam)
{
    HDC hdc = GetDC(hWnd);  
    SelectObject(hdc, GenerateColor());
    
    if(code == 1)
    {
        Ellipse(hdc, x, y, x + 200, y + 200);   
    }
    else if(code == 2)
    {
        Rectangle(hdc, x, y, LOWORD(lParam), HIWORD(lParam));
    }
    else 
    {
        MoveToEx(hdc, x, y, NULL);
        LineTo(hdc, LOWORD(lParam), HIWORD(lParam));    
    }
    
    ReleaseDC(hWnd, hdc);
}

 #include <windows.h>
 
#ifdef BUILD_DLL
   #define EXPORT __declspec(dllexport)
#else
   #define EXPORT __declspec(dllimport)
#endif
 
EXPORT int Random(int min, int max);
EXPORT HBRUSH GenerateColor();
EXPORT void PaintFigure(HWND hWnd, int code, int x, int y, LPARAM lParam);