Concatenating

You can use "+" for concatenation although it is not recommended as this is a WordBasic operator. You should use "&".
When using the string concatenation character "&" be sure to insert a space before and after this operator.

String Concatenation (&)

This operator can be used to join two or more strings together.
This operator can also automatically convert between types as it combines a resultant string.
It can be used to combine several different variable types into a string without any explicit conversion.

Dim sMyLongString As String 
Dim sShortString As String 
sShortString = "Monday" 
sMyLongString = sShortString & " " & "some more text" 
MsgBox sMyLongString     ' = "Monday some more text"  

String Concatenation (+)

This can also be used as a string addition operator to join two or more strings together.
If you try to use this operator with multiple variables types you will receive a "Type Mismatch" error.

Dim MyNumber As Variant 
MyNumber = "2" 
MyNumber = MyNumber + MyNumber + MyNumber 
MsgBox MyNumber  ' "222"  

JOIN Function

JOIN - Returns a text string containing all the elements in an array (String).

Dim aValues() As String 
aValues(0) = "string1" 
aValues(1) = "string2" 
aValues(2) = "string3" 
Debug.Print Join(aValues)        '= "string1 string2 string3"   

Large String Concatenating

When you are concatenating in a large loop, in excess of a few thousand times always use the JOIN function.

' instead of this
Dim myString As String 
For i = 1 To 10000 
   myString = myString & myArray(i) 
Next 

' use this approach
Dim myString As String 
ReDim temporary(1 To 10000) 
For i = 1 To 10000 
   temporary(1) = myArray(i) 
Next 
myString = Join(temporary,"")