[oneD] use enum for constants

include/cantera/oneD/StFlow.h

@@ -19,13 +19,16 @@ namespace Cantera
 //   constants
 //------------------------------------------
 
-// Offsets of solution components in the solution array.
-const size_t c_offset_U = 0; // axial velocity
-const size_t c_offset_V = 1; // strain rate
-const size_t c_offset_T = 2; // temperature
-const size_t c_offset_L = 3; // (1/r)dP/dr
-const size_t c_offset_E = 4; // electric poisson's equation
-const size_t c_offset_Y = 5; // mass fractions
+//! Offsets of solution components in the 1D solution array.
+enum offset
+{
+    c_offset_U   //! axial velocity
+    , c_offset_V //! strain rate
+    , c_offset_T //! temperature
+    , c_offset_L //! (1/r)dP/dr
+    , c_offset_E //! electric poisson's equation
+    , c_offset_Y //! mass fractions
+};
 
 class Transport;