Chandra,
If you want to output a set number of updates then stop, you would want to use single buffer.
If you are looking for continuous generation then double buffering will be the preferred method. There are examples of both at:
http://zone.ni.com/devzone/devzone.nsf/webcategories/BF1AC4565B4D356486256797004CBD45?opendocument&node=dz52313_us
They will be a great help in getting you started. I recommend specifically looking at the Double Buffered Waveform Analog Output example in V C++.
Hope this helps.
Kevin R
Applications Engineer
National Instruments