I believe 'u' was implemented some time ago, so your version must be very old, you should update it, its free.

vec_for_uv works in all versions. But when you omit parameters in an example, it of course will crash because then, the functions dont get valid parameters.

You will see that there are two sorts of examples in the manual. The newer functions have full examples that you can directly copy-paste in your code, or they are even full programs. Older functions have short examples that only show how to use the function. They are not copy-paste and require that you understand what a parameter is used for and so on. For instance, the vec_for_uv example expects that you have a global vector "temp" defined somewhere, like many other examples.

Just some advice, I would NOT "move on" when something does not work. You have to understand why it does not work. There is ALWAYS a good reason. I cant see it either in your code but thats why you have a debugger. If you just ignore a problem in your code because you dont see it at first, the problem will stay, and will affect your code further, causing delays, frustration and so on.

Make sure that you code works 100% and not only 90%. When there is an unexplained delay or you have to press a key several times, dont give up until you found the reason, and then you'll say "Ah, why didnt I see it at first?" Maybe you have several entities "Panzer" in your level, but your function only works when there is only one. Or something like that.

Just some piece of advice from a fellow programmer who made the very same experiences with the first steps of programming.