Index: mttroot/mtt/lib/cr/hh/pressuredrop.hh
==================================================================
--- mttroot/mtt/lib/cr/hh/pressuredrop.hh
+++ mttroot/mtt/lib/cr/hh/pressuredrop.hh
@@ -1,17 +1,18 @@
 #ifndef PRESSUREDROP_HH
 #define PRESSUREDROP_HH
 
-#include <math.h>		// fabs, pow
+#include <cmath>		// fabs, pow
+#include <string>
 
 #include "constants.hh"
 #include "frictionfactor.hh"
 #include "kinematicviscosity.hh"
 #include "sign.hh"
 
 inline double
-pressuredrop(const string fluid,
+pressuredrop(const std::string fluid,
 	     const double d,
 	     const double l,
 	     const double r,
 	     const double rho,
 	     const double T,
@@ -24,11 +25,11 @@
   double dP = k * 8.0 * rho * pow(Q, 2) / (pi2 * pow(d, 4));
   return (dP * sign(Q));
 }
 
 inline double
-pressuredrop(const string fluid,
+pressuredrop(const std::string fluid,
 	     const double d,
 	     const double l,
 	     const double r,
 	     const double rho,
 	     const double T,