Simple challenge VII for the simpleton Feeb

You recently claimed "There are *no* competent C programmers here (except little ol' me)."
It's long past time for you to begin trying to prove your programming competency (you NEVER have, in any language).
Write one C routine that will compute the 3 quartiles of any dataset of positive integers.  Quartiles subdivide the datasets into 4ths by median.
Here are some random datasets to work from.
N = 20:
3 9 9 12 17 22 29 29 33 35 36 37 40 44 46 49 50 51 55 57
N = 21:
3 3 4 4 4 7 8 9 13 17 30 32 34 36 38 42 43 43 45 48 54
N = 30:
6 12 13 17 19 20 20 20 22 23 29 32 34 40 41 42 44 46 48 50 61 64 66 68 69 72 73
N = 31:
6 10 10 15 19 21 21 31 36 42 44 48 50 50 51 52 58 62 68 69 70 70 72 76 81 82 82 84 84 92 93
Use this method:
Q1 = median of lower half not including Q2
Q2 = median of dataset
Q3 = median of upper half not including Q2
Example
1 2 3 4 5 6 7 8 9 10 11
Q1 = 3
Q2 = 6
Q3 = 9
I've already written such code, in C and python.  And I posted both to clc, so don't cheat and plagiarize it from there or elsewhere as you often do.
See you NEVER, fraudulent lying asshole.