on recent MS compilers one must include stdlib.h before glut.h
diff --git a/demo/simple.cpp b/demo/simple.cpp
index d17c5ab..b4d8826 100644
--- a/demo/simple.cpp
+++ b/demo/simple.cpp
@@ -27,6 +27,8 @@
#include <math.h>
+#include <stdlib.h> // exit()
+
#if defined HAVE_GL_GLUT_H
# include <GL/glut.h>
#elif defined HAVE_GLUT_GLUT_H