Test:

str="it is a testing question"
Call spacecount(str,d)  /*Function Call*/
msgbox "Number of spaces:" & d

User Defined Function : 

Public function spacecount(a,b)
 str=a
 p=split(str)
 coun=0
For i=1 to ubound(p)
 coun=coun+1
Next
 msgbox coun
 b=coun /*Returns Number of spaces to the calling Function /
End Function