A Plague of Rabbits

I have a terrible rabbit problem.

I used to have a pair of baby rabbits; they were extremely cute and fluffy, so of course I got them. But the shopkeeper I get them from – a guy named Leonardo, of Pisa Pets – didn’t tell me they would mature very fast, and breed even faster.

After a month, I had a mature pair of rabbits… and, of course, they bred. Damn.

So, a month later, I had a pair of adults and a pair of baby rabbits.

And a month later, I had two pairs of adults, and another pair of baby rabbits,

And a month later, I had three pairs of adults, and two pairs of baby rabbits.

And a month later, I had five pairs of adults, and three pairs of baby rabbits.

HELP! I HAVE SO MANY RABBITS, I’M GOING HOPPING MAD!

I know that the number of rabbits I have each month will be the number of rabbits I had in the previous month, plus the number of rabbits I had in the month before.

Given I started with, well, no rabbits, and I got one pair of baby rabbits, write a function that tells me how many rabbits I’ll have after $n$ months. Give it this prototype:

long long rabbits (long long month);

(Hint: $\mathrm{Rabbits}_n = \mathrm{Rabbits}_{n - 1} + \mathrm{Rabbits}_{n - 2}$.)

To run some simple automated tests:

$ 1511 autotest rabbits

To run Styl-o-matic:

$ 1511 stylomatic rabbits.c
Looks good!

You’ll get advice if you need to make changes to your code.

Submit your work with the give command, like so:

$ give cs1511 wk12_rabbits

Or, if you are working from home, upload the relevant file(s) to the wk12_rabbits activity on Give Online.