dim n,m 
n=inputbox("input a number:","recursion") 
m=factorial ( n ) 
if n<0 then msgbox "must be input a number bigger 0." 
elseif n=0 then msgbox "0"&"!"&"is:"&"0" 
elseif n>0 then msgbox n&"is:"&m 
rem how to done not input and press sure case. 
end if 
Function Factorial (N) 
If N <= 1 Then Factorial = 1 
Else Factorial = Factorial(N - 1)*n^n 
End If 
End Function