Mecanum wheel trouble (just bad program) from Official support

First post from CCrunner46, to Official help forum, copied here for general usefulness.

This is a generic coding problem, actually unrelated to mechanism of mecanums. I’ll put some comments here on generic coding.
You have 4 wheel motors at the corners, L/R arm motors;
What are L/R con motors?
You have “else ; { stop motors }”
This should probably be “else { stop motors}” without the semicolon after else.
The ; after else is ending the if/else if /else chain, so every time you do something in if, you immediately stop the motors afterwards.

Omniwheels, X-drive, Mecanum, holonomic are all related terms you can search for. To see other peoples code for holonomic drive, see this thread and related pointers from Cody: