C ++ DLL call from C #

I want to use a C ++ DLL from C #. C ++ DLL is a win32 console application. I have successfully called it and want to process the data I have from C ++ to C #. However, the C # application exits the DLL execution and this line:GetArrayFromDLL();

I am new to C # and Visual C ++. Can anyone give some suggestions?

thank

namespace ConsoleApplication1
{
    class Program
    {

        [DllImport("Lidar_DataCal_CDLL.dll")]

        public static extern void GetArrayFromDLL();



        static void Main(string[] args)
        {
            Console.WriteLine("This is C# program");
            GetArrayFromDLL();
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());

        }
    }
}

      

        
        
        
      

    

It is a DLL written in a win32 application.

extern "C"
{
  __declspec(dllexport) void GetArrayFromDLL()
  {

/// Reading hex from a file 

  FILE * pFile;

  FILE * f;

  signed int array_data[81],array_data1[81],i;

  double fangle,fsin,fcos,fangle_rad;

  double afx[81],afy[81];

  int px,py;

  char file_read[20] = "scandataset1.txt";

  char file_write[20] = "xycordinates1.txt";


  pFile = fopen ( file_read,"a+");

  if (pFile != NULL)

      {
  for (i=0;i<80;i++)

      {
       char buffer[3];

       fscanf (pFile, "%x",&array_data[i]);

      sprintf ( buffer ,"%d", array_data[i]);

      printf ( "I have read: %s \n\n", buffer);

      array_data1[i] = atoi(buffer);

       // finding angle 

       fangle = 20 -( (i+1-1)*0.5);

       fangle_rad = (PI*fangle/180);

       fsin = -sin(fangle_rad);

       fcos =  cos(fangle_rad);

       afx[i] = array_data[i] * fsin;

       afy[i] = array_data[i] * fcos;

      // printf ("X: %lf  and Y: %lf  \n\n",afx[i],afy[i]);

       f = fopen(file_write,"a+");

       if(f != NULL);

       fprintf(f,"%lf %lf\n",afx[i],afy[i]);

       fclose (f);

      } 
      }
  else
      {

      printf("Error opening fail");

      }

  fclose (pFile);
      }

    }