Tldr is that when you hear/read just the noun or verb itself you can already infer a lot of information about who is doing the act and what is the act being done to.
For more informaion feel free to read about conjugation and declination.
Yes, it gets pretty complex.
You have to make it easy on yourself and just use a switch with default true for evens, then handle all the odd numbers in individual cases. There, cut your workload in half.