Sub phoenixmoto()
With UserForm1
.wow.Value = True
With .comb
.AddItem "addition"
.AddItem "subtraction"
End With
.comb.Value = "subtraction"

.TextBox1.Value = 10
.TextBox2.Value = 20
.TextBox3.Value = 30
.Show
End With
Unload UserForm1
End Sub



Private Sub cancel_Click()
hide
End Sub


Private Sub ok_Click()
Dim a As Variant, b As Variant, c As Variant
If TextBox1.Value = "" Then
MsgBox "a field is empty"
Exit Sub


End If
If TextBox2.Value = "" Then
MsgBox "b field is empty"
Exit Sub
End If
If TextBox3.Value = "" Then
MsgBox "c field is empty"
Exit Sub
End If

a = TextBox1.Value
b = TextBox2.Value
c = TextBox3.Value

If wow.Value = True Then
Select Case comb
Case "addition"
Call ad(a, b, c)
Case "subtraction"
Call minus(a, b, c)
End Select
End If
hide
End Sub


Sub ad(a As Variant, b As Variant, c As Variant)
ThisDocument.TextBox10.Value = amrit(a, b, c)
End Sub
Sub minus(a As Variant, b As Variant, c As Variant)
ThisDocument.TextBox10.Value = sam(a, b, c)
End Sub
Public Function amrit(a As Variant, b As Variant, c As Variant) As Variant
amrit = (a + b + c)
End Function
Public Function sam(a As Variant, b As Variant, c As Variant) As Variant
sam = (a - b - c)
End Function

here in this code function sam works fine and delivers -40 as answer but function amrit does concatination(102030) instead of sum(i.e 60)
how + symbol is working like &