ASSERT
 - “Assert is a comment that cannot lie.”
 - Documents what you expect to be true… and enforces that it *must* be true.
 - If the condition is false, then program will crash---and that is very good.
 - Helps you catch a problem close to the source (i.e., the mistake in your code).
 - Code can test itself as it runs.
 - Assert is not a substitute for unit testing.
   - It is a supplement to your testing.
   - It is a better way to write comments that state what should be true at a certain line.

How to use:
- #include <assert.h>
- assert(«condition»);
- condition must be true if the code is correctly written (i.e., no mistakes).
- condition should be something that YOU have complete control over.

Do not use assert…
- To check arguments passed from external code (i.e., other people's code).
- To check environmental conditions (e.g., file exists, file is readable, etc.).

Assert is a programming thing, not a C-specific thing.