[Alessandro_Lamberti]

Hy everyone, i'm trying to define an udf for mass transfer between a discrete phase and a continous phase.
The udf is defined as follows:
#include "udf.h"

DEFINE_SOURCE(coupled_mass_transfer, cell, thread, from_species_index, to_species_index)
{
real C_bulk, C_interface, mass_transfer_rate;
real Re, Sc, Sh;
real rho, mu, D;
real droplet_diameter, flow_velocity, droplet_velocity;
real vapor_diffusivity;
real **C_vapor_bulk, **C_vapor_interface;
real vapor_transfer_coeff;

rho = C_R(cell, thread);
mu = C_MU_L(cell, thread);
D = mu / rho;
droplet_diameter = C_UDMI(cell, thread, 0);
flow_velocity = C_UDMI(cell, thread, 1);
droplet_velocity = C_UDMI(cell, thread, 2);
Re = rho * (flow_velocity - droplet_velocity) * droplet_diameter / mu;
vapor_diffusivity = 1e-5;

Sc = mu / (rho * vapor_diffusivity);
Sh = 2 + 0.6 * pow(Re, 0.5) * pow(Sc, 1.0/3.0);
vapor_transfer_coeff = Sh * D / droplet_diameter;
C_bulk = C_YI(cell, thread, from_species_index);
C_interface = C_YI(cell, thread, to_species_index);
C_vapor_bulk = C_UDMI_POINTER(cell, thread, 3);
C_vapor_interface = C_UDMI_POINTER(cell, thread, 4);
mass_transfer_rate = vapor_transfer_coeff * rho * (**C_vapor_bulk - **C_vapor_interface);

source = -mass_transfer_rate;

return mass_transfer_rate;
}

but when i compile it on fluent it says line 25: non-integer subscript expression: pointer to float.

can anyone help me?
Thanks