How can I make a variable always equal to the result of some calculations?

Question

In math, if z = x + y / 2, then z will always change whenever we replace the value of x and y. Can we do that in programming

Answer 1

What you're describing is late binding, which a compiled language like C++ can do only with difficulty. In an interpreted language, all you need is the ability to set z to an unevaluated expression and delay binding of z's value until the calculation is needed, typically signaled by a call to a function that forces the evaluation such as eval in Lisp. In my Expert System's rules language, I have not only eval but noeval, which protects its argument from one level of evaluation. That provides granular control over the binding, with some sub-expressions being evaluated (bound) and others not, if desired. This is not applicable to your scenario, but it sets the scene in terms of the language landscape.