You have several options here. Maybe two of the easiest are either OPC or MS-Excel.
1) you could write a quick little OPC client and interface that with the DeltaV OPC server.
2) if you can get the data from your Fortran/C calcs into Excel then you could run excel on your DeltaV app station and use the DeltaV Excel-Addin to pass data back and forth in real-time.