A fixed-capacity circular queue

Problem

Implement a queue of int on a circular array of fixed capacity, with fields data, front (index of the oldest element, initially 0) and size. The array never grows.

enqueue stores at (front + size) % capacity;
dequeue returns data[front] and sets front = (front + 1) % capacity.

Input: the capacity (≥ 1) on the first line, then one command per line until the input ends:

Command	Output
`enqueue x`	nothing, or `full` if the queue already holds `capacity` elements (x is then discarded)
`dequeue`	the removed value, or `empty`
`peek`	the front value without removing it, or `empty`
`size`	`size <n>`
`print`	`front=<front index>` followed by the elements from front to back, e.g. `front=2 [30, 40, 50]`

Example with capacity 3:

enqueue 1
enqueue 2
enqueue 3
enqueue 4
print
dequeue
enqueue 4
print

prints

full
front=0 [1, 2, 3]
1
front=1 [2, 3, 4]

(4 was stored in slot 0: the queue wrapped round.)

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