C: System calls and pointers to reverse a file - c

Question

Solved. Thanks lutogniew.....just over complicating it...
So I am having some trouble with a homework assignment. The assignment is to take in a file (using only system calls), reverse it and write an output file with that reversed data on it (ASCII only). A catch is that the reverse section has to be done with pointers. I did the following below, which does work. However, it does not use pointers to reverse.
My question I guess, is how can I access something like data[] using pointers? Or, how can I read from the file into it. Everything I tried (mostly char**) only reads in null.
Any help would be much appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
int main(void)
{
int i = 0;
int fileOut = open("output.txt", O_WRONLY | O_APPEND);
int fileIn = open("input.txt", O_RDONLY);
int start = lseek(fileIn, 0 , SEEK_CUR);
int end = lseek(fileIn, 0 , SEEK_END);
int restart = lseek(fileIn, 0-end , SEEK_CUR);
char data[end];
char reverseData[end];
read(fileIn, data, end);
for(i = 0; i< end; i++){
reverseData[i] = data[end-(i+1)];
}
write(fileOut, reverseData, end);
return 0;
}

Answer 1

After Accept Answer.
Something for OP to consider as another approach:
For fun, a not-so-serious recursive approach to reverse the file.
void reverse(int fileIn, int fileOut) {
char data;
if (read(fileIn, &data, 1) == 1) {
reverse(fileIn, fileOut);
write(fileOut, &data, 1);
}
}
int main(void) {
int fileOut = open("output.txt", O_WRONLY | O_APPEND);
int fileIn = open("input.txt", O_RDONLY);
reverse(fileIn, fileOut);
close(fileIn);
close(fileOut);
return 0;
}

Answer 2

You must understand that what is presented to you as an array in C, in reality is just a pointer, pointing to the beginning of the memory belonging to that array. This snippet should make everything quite clear:
int test[] = { 1, 2, 3 };
int* ptr = test + 2; // ptr now points to the third element
EDIT
As for loading data into an array: again, remember that array itself is just a pool of memory (a buffer) - it begins where the pointer mentioned above points to, and has the size equal to numberOfElements * sizeOfSingleElement. Now look at the signature of the read function:
size_t read(int fildes, void* buf, size_t nbytes);
It reads nbytes into buffer pointed to by buf. Rings a bell?