What are problem credits?
When your students run check their code it runs on one of a series of servers to compile and execute the code. Most of the time you'll need a problem credit for that to happen. There are a few exceptions. More on that below.
Basically you're purchasing a set of credits so that your students can run their code.
Do credits expire?
If you purchase a block of credits, they are yours to use. They don't expire at the end of the month. There's not an expiration date.
You Said Exceptions
There are a couple of cases where your students can submit problems without you needing any purchased credits.
The first is if you're using one of the free problems. These are the problems that are in our public online problem library. You can create assignments based on these problems and they won't count against your credits. If you find enough in the free library for your students you can use ClassCube without ever purchasing credits. We do think that once you find out how great ClassCube is though you'll want to explore other problems.
And, each month we put 1,000 credits into every account. You can use these on any problems you like and they'll be used before any credits you've purchased. Depending on how many students you're working with 1,000 credits a month may be more than enough.
How many credits do I need?
Looking at our data it looks like the students average about 11.5 submissions per assignment.
This is across all the problems ranging from simple warm-up style return methods to complex AP FRQ style questions. So if you're focusing more on the simpler problems then your average will probably be less per student. If you're using ClassCube only for the more complicated problems it'll bump up your average.
What happens if I run out?
If you've purchased credits then your account will have a 500 submission buffer before there's an issue. Instead of blocking submissions, the first 500 will go through. Once the 500 are spent submissions will stop working and you and your students will get messages that your account is out of credits.
If you've never purchased credits then this buffer is not there and your submissions will stop when you get down to zero.
What about problems I create?
Credits work exactly the same way whether you're using one of our problems or a problem you create.
Do you offer unlimited plans?
Yes we do. See our page on unlimited submission plans for more information.
Did we miss something? Start up a conversation on our support forums and let us know what we can do to help.