how can i add error checking to thisvba code to check that it runs
well.

Sub test()
Dim x As Single, n As Integer, i As Integer, fact As Integer
n = Range("b3")
x = Range("a3")
'calculate n factorial
'checking B3
If Range("B3") <= 0 Or Int(Range("B3")) < Range("B3") Then
MsgBox " integer in b3 must be greater then zero"
Exit Sub
End If
fact = 1
For i = 1 To n
fact = fact * i
Next i
'calculate result x ^ n/fact n!
result = x ^ n / fact
Range("c3") = result

End Sub