# Erle Robotics C++ GitBook

## Preprocessor Macros

We’ve seen how to define constants using the preprocessor command #define. We can also define macros, small snippets of code that depend on arguments. For instance, we can write:

 # define sum (x, y) (x + y)


Now, every time sum(a, b) appears in the code, for any arguments a and b, it will be replaced with (a + b). Macros are like small functions that are not type-checked; they are implemented by simple textual substitution. Because they are not type-checked, they are considered less robust than functions.