Can any one tell me is it OK to include other subroutines (Calculate some values and return the values into the UDF main) in the UDF? I tried once, but it seems it couldn't be complied. BTW, I am using the EXPRESS VC++ .

yes is ok, I have a main file a header file and a functions file and it works fine.

what does this message mean?: "udf limitation: Intensity: prototypes must appear outside the function body."

'Intensity' is a subrountin in my UDF.

in your header file you should declare the prototype of your function (what parameters take, if return a value), or if you don't have a header file after the #include statements put your function prototype.