It's undefined behavior, at least. It probably causes a segmentation fault and crashes. At worst, it will seem to work but will corrupt some other data when you write to such an index.

You can find out if you either "Train Again" or hit "Fork" and change the tests to use any higher number within the array. I just tried it and it died with

Test Crashed
Caught unexpected signal: SIGSEGV (11). Invalid memory access.

I can not see checking for "order[i]>63". But in this code I see "int num[64] = {0}". What result of using num[68] for example?

Which other confused person is running around putting Spoiler flags on boilerplate and C programming discussion?

int num[MAX_INT] = {0}; doesn't fit into the stack.

You could do int *num = malloc(MAX_INT) but you might get fired. I would fire you.

edit: it's INT_MAX, actually. I forgot :P

Excellent complexity. Large Allocations, where your solution benefits the most, shouldn't use VLAs. Large Stack Allocations will fail.