Updates from pull request #4

Author: cpp-tutor

headers/02-constexpr.cpp

@@ -4,6 +4,9 @@
 #include <cmath>
 using namespace std;
 
+// Note: currently, not all compilers mark `acos` as a
+// constexpr function in cmath. The following line might
+// not compile with `clang++` for example.
 constexpr double PI1 = acos(-1.0);
 constexpr double PI2 = 22.0 / 7.0;
 

modules/02-constexpr.cpp

@@ -3,6 +3,9 @@
 import std;
 using namespace std;
 
+// Note: currently, not all compilers mark `acos` as a
+// constexpr function in cmath. The following line might
+// not compile with `clang++` for example.
 constexpr double PI1 = acos(-1.0);
 constexpr double PI2 = 22.0 / 7.0;