It is a best practice for a $.$ h header file to begin with a preprocessor directive like wifndef SHAPE H$\_$

and end with another directive like

Hendif $\frac{?}{?}$ SHAPE$\_$H$\_$

Why is this a best practice?

It prevents compile errors in the cwent that a orgect has two headers with the same fiename.

It allaws the compier to optimize the code, makng progrents run fasler.

It prewents campile errors in the event that a progect has two variables w th the same unntifer.

In prevents runtime errors in the event that an undefined funcion is called:

It prevents compila crrars in the event then the headar is included multiple limes$.$