Step-69: add missing include cmath

diff --git a/examples/step-69/step-69.cc b/examples/step-69/step-69.cc
index fca2a20386d98d776911df49a804ed1edb84238e..f0d4744c2566c1353c80234e48681c5131c869c8 100644 (file)
--- a/examples/step-69/step-69.cc
+++ b/examples/step-69/step-69.cc
@@ -82,6 +82,9 @@
 #include <boost/range/irange.hpp>
 #include <boost/range/iterator_range.hpp>
 
+// For std::isnan and std::isinf.
+#include <cmath>
+
 // @sect3{Class template declarations}
 //
 // We begin our actual implementation by declaring all classes with their