Although you can also use the + operator to concatenate two character strings, you should use the & operator for concatenation to eliminate ambiguity and provide self-documenting code.
When you use the + operator, you may not be able to determine whether addition or string concatenation will occur.
The underlying subtype of the expressions determines the behavior of the + operator in the following way:
|Both expressions are numeric
|Both expressions are strings
|One expression is numeric and the other is a string
If one or both expressions are Null expressions, result is Null. If both expressions are Empty, result is an Integer subtype. However, if only one expression is Empty, the other expression is returned unchanged as result.