This is an early version of a program that computes the length of the hypotenuse of a right triangle given the lengths of two sides of the triangle.
The successor program is named Pythagoras 2.0
Both programs show how to use macros leading to code that is more readable, more organized, and better maintainable.
Functions are commonly used to partition the code of a function. Macros can also partition a large code section, but macros are not heavy users of system resources like function are. As a programmer the use of macros should be in your collection of programming tools.