c# help req on unmanaged DLL C function

Question

Hi all,

     i am working on a C DLL which takes all inputs as pointer values...unmanaged code

      [DllImport("Ziee_Mask.dll")]
      unsafe public static extern void IQ_Data_to_Spectrum(double* Spec, double* Real, double* Img, Int32 len);

      where the inputs are real and img values should be read from a excel sheet and provided as input around 65536 values ...len is 65536(length)  ..

      output is a array of data in  "spec"  ...

       i need to store the input data from excel sheet and pass to function and take output from spec and store it

       i tried some of the ways which ends up in hanging of forms ...I am new to c sharp....Somebody please help me...