LabVIEW comes with a pdf file titled "Using external code in LabVIEW", which provide good references on how to do what you are asking. In case you don't have it, you can download it from ni.com:
http://digital.ni.com/manuals.nsf/web_productcurrent/4F1447F7CD83D6D88625690D00637CED?OpenDocument
There is a small issue with MS Visual C++ 6.0, which is addressed in the following link:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/d7bdb30eef410056862569ab00724294?OpenDocument
Here is also a full tutorial about CIN at ni.com:
http://www.ni.com/support/labview/program/callcode/cinmain.htm
Also check the following examples, which were very useful for me:
Using a CIN to Create an Array of Strings in LabVIEW
http://zone.ni.com/devzone/devzoneweb.nsf/ope
ndoc?openagent&AD517F5DCCAF70228625683A000A570F&cat=2F4F574886553A62862567AC004F032D
CIN that converts a LabVIEW String to a C String, Modifies it, and Returns it as a LabVIEW String
http://zone.ni.com/devzone/devzoneweb.nsf/opendoc?openagent&D978409908EA760D8625683A000B6B6E&cat=2F4F574886553A62862567AC004F032D
Replacing a Portion of an Array
http://zone.ni.com/devzone/devzoneweb.nsf/opendoc?openagent&3B5B43568CF83D948625683A000C397E&cat=71359FBAD517F4CB862567E0007B6F6E
Best regards;
Vargas
www.vartortech.com