#define DUMMY
I'm not totally sure what you're asking, but I think you're referring to a dummy variable. A dummy variable is just a variable that you don't need, but that you use to make the calculation more clear. You would declare it like any other variable. In the following example, time is a dummy variable
Code:
// calculate position: x = x0 + v0 * t + 1/2 * a * t^2
// no dummy variable
x = x0 + v0 * (end_time - start_time) + 0.5 * a * (end_time - start_time) * (end_time - start_time);
Code:
// calculate position: x = x0 + v0 * t + 1/2 * a * t^2
// with dummy variable, much cleaner
int time = end_time - start_time;
x = x0 + v0 * time + 0.5 * a * time * time;