JSL also provides operators for in-place arithmetic, or assignment operators. These operations are all done in place, meaning that the result of the operation is assigned to the first argument. The most basic assignment operator is the = operator (or the equivalent function Assign). For example, if a is 3 and you do a+=4, then a becomes 7.
The first argument to an assignment function must be something capable of being assigned (an L-value). You cannot do something like 3+=4, because 3 is just a value and cannot be reassigned. However, you can do something like a+=4, because a is a variable whose value you can set.
Add To(a, b)
Adds a and b and places the sum into a.
Must be ...