Changed darr_at to return a pointer

lib/darr.c

@@ -51,12 +51,12 @@ void darr_append_bytes(darr_t *darr, byte_t *bytes, size_t n)
   darr->used += n;
 }
 
-byte_t darr_at(darr_t *darr, size_t index)
+byte_t *darr_at(darr_t *darr, size_t index)
 {
   if (index >= darr->used)
     // TODO: Error (index is out of bounds)
-    return 0;
-  return darr->data[index];
+    return NULL;
+  return darr->data + index;
 }
 
 void darr_write_file(darr_t *bytes, FILE *fp)

lib/darr.h

@@ -119,7 +119,7 @@ void darr_append_bytes(darr_t *darr, byte_t *b, size_t n);
 
    @return Byte at the nth position, or 0 if n is an invalid index
  */
-byte_t darr_at(darr_t *darr, size_t n);
+byte_t *darr_at(darr_t *darr, size_t n);
 
 /**
    @brief Write the bytes of a dynamic array to a file pointer