--- a/cppdatabase.cc
+++ b/cppdatabase.cc
@@ -30,7 +30,7 @@
 
     struct Person p;
 
-    while ((in.read ((char *)&p, sizeof (Person))) != NULL) {
+    while ((in.read ((char *)&p, sizeof (Person))) != 0) {
         std::cout << p.lastname << ", " << p.firstname << ", " <<
             p.position << std::endl;
     }