A few functions require passing an argument containing a single character, such as pipt_nextptwsource. To pass such a value, declare the argument as an integer, then assign the ASCII value of the character using the Asc function.
Dim src As Integer
src = Asc("F")
Functions that return a single character such as pipt_pointsource declare the receiving variable as a string of length 1.
Dim source As String * 1
status = pipt_pointsource(pt, source)