C :: Passing Files To Function?

I need to pass a file as a parameter to the get_corners function, and then fill an array with an unknown quantity of data, and return the number of data to main.

Compiling this generates some messages about unused variables, which is fine for this incomplete code.

Running it just generates a blank screen. So that obviously needs to be fixed. What am I doing wrong?

I have tried moving fpin = fopen ("c: emphw12.txt","r"); to the main function, then function call to get_corners, and then closing the file after return, but same blank screen.

hw12.txt is simply:
4,0,4,7.5,7,7.5,7,3,9,0,7,0,4,0

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
FILE *fpin; // input file

[Code].....