You get the error because the variables are in two different data types.
You have two options. You can either convert the string value to number format, or you can convert the number value to string.
Depends on what you want to get as the output. If both are in string, it will not add the values, but it will concat them.
If both are in integer, it will add the values…
Try these two… String to integer Int32.Parse(StringVariable)
Converts string value to integter
integer to string intVariable.ToString
Applying to your expression
Ex: C = 1, A = “2” C + Int32.Parse(A) result is: 3
Just another basic question … how do I copy the error comments from studio… I managed to do it on this one but unable to recall how I managed to do it…