geographic to projected (but i dont know which zone )

[AbdulrahmanAlqasim]

i have big map in geographic coordinates (WGS84) . when the user click on the map, i want to convert the point coordinates(where the user clicked)  from geographic to projected (utm).

see this line:
IProjectedCoordinateSystem pcs = srFactory.CreateProjectedCoordinateSystem((int)esriSRProjCSType.esriSRProjCS_NAD1983N_AmericaLambert);

my problem is that i dont know to which utm zone i should put. because the map contain many utm zones (around 24 zones)

so how i can project the coordinates when i dont know the exact zone ?

thank you

[KirkKuykendall]

see http://gislounge.com/how-to-calculate-the-boundaries-of-an-utm-zone/