Error cannot be detected?

Sub DetermineErrMsg()

Dim selr As Integer

selr = Selection.Row

On Error Resume Next

Range("c" & selr) = Range("a" & selr) + Range("b" & selr)

If Err.Number <> 0 Then 'There is an error
    If Err.Number = 13 Then
    MsgBox "Please type a number in the box"
    End If
Else: MsgBox "There is no error"


End If

End Sub

http://s24.postimg.org/ncebpkbwz/excelvba.jpg

Hello everyone! I don't know why excel cannot detect an error when I put texts in Cell A4 and B4. It just returns the combined texts in Cell C4. However, an error can be found when I put a number in Cell A3 and texts in Cell B3. Thanks for your help in advance.

I think this is because you can't mix and match. Adding two bits of text is permissible - it's just treated as concatenation - but adding a number and a text confuses Excel as it wants to treat the number in one way and the text in another, rather like trying to add an apple and an orange. That is my non-technical suggestion. What are you actually trying to do?

Originally Posted by StephenR

I think this is because you can't mix and match. Adding two bits of text is permissible - it's just treated as concatenation - but adding a number and a text confuses Excel as it wants to treat the number in one way and the text in another, rather like trying to add an apple and an orange. That is my non-technical suggestion. What are you actually trying to do?

What I am trying to do is I hope excel is able to detect there is an error once either two cells or one of the cells are put into texts.