Code for mesh generation
 

I want to know how to write codes for generating mesh in 3-D geometry for flow analysis in softwares like fluent. I have been using Gambit for the mesh generation but i want to know whether using Gambit is good or generate gode for the geometry by codes and moreover the geometry will be imported from parasolid or such softwares. so I need a guideline so that i can generate meshes for my geometry accordingly.