Questions about GPIO

[limitlesscodes]

Hey Pine64 backers! I am having difficulty figuring out how I would use C to take user input, button presses, and light LEDs with the GPIO, I understand C fairly well but have no experience with interfacing with"GPIO." Here is the best program I could think of although I believe there is a much better way to do this:

Code:

/*
*Simple pulsing of GPIO example
*/
#include <stdio.h>
#include <string.h>

FILE *zero, *one;

int main(int argc, char *argv[])
{

zero = fopen("/sys/class/gpio/gpio206/value", "w");
one = fopen("/sys/class/gpio/gpio206/value", "w");

while(1)
{
fputs("0\n", zero);
fflush(zero);
fputs("1\n", one);
fflush(one);
}
}

Also what determines the pin number? Thanks for your help!