Convert Code from .m to .c

I am trying to convert my .m code into .c by building MEX file. Now for following loop it is giving me error for n. I already defined n as extrinsic.

for i=1:(n-1);

      Fend=kron(Fend,F);

end;

Error: Expected either a logical, char, int, fi, single, or double. Found an mxArray. MxArrays are returned from calls to the MATLAB interpreter and are not supported inside expressions. They may only be used on the right-hand side of assignments and as arguments to extrinsic functions

[Walter Roberson]

Wow, why would you do that?