pointers.c

#include <stdio.h>
int main(){
  fprintf(stderr, "%s\n", "Study of int arrays");
  fprintf(stderr, "%s\n", "===================");
  int a[] = {1, 2, 3, 4, 5};
  // Arrays are contiguous memory locations.

  // The variable holding the array actually points to
  // the first item in the array :
  fprintf(stderr, "%p == %p\n", a, &a[0]);
  // Add 1 to this pointer and you point to the second item
  // in the array, ie, the next integer in the contiguous memory
  // NOTE! The next integer was stored 4 bytes after the first
  // integer. So integer pointer KNOWS that when you add 1 to it,
  // it should move 4 places.
  fprintf(stderr, "%p == %p\n", a + 1, &a[1]);

  // Interesting to note that you can get any item in the array
  // if you have a pointer to an item in the array.
  fprintf(stderr, "%d == %d\n", a[0], *(a + 0));
  fprintf(stderr, "%d == %d\n", a[1], *(a + 1));

  fprintf(stderr, "\n\n");
  fprintf(stderr, "%s\n", "Study of char arrays");
  fprintf(stderr, "%s\n", "===================");
  // Let's see how character pointers work
  char c[] = {'a', 'b', 'c', 'd', 'e'};
  // Print the address of first item in character array
  fprintf(stderr, "%p == %p\n", c, &c[0]);
  // Print the address of second item in character array
  // NOTE! The next character was stored just 1 byte after the
  // prev character because chars occupy only 1 byte of mem.
  // So the character pointer just KNEW that if you add 1 to it,
  // it should go to a memory location just 1 byte after where it
  // was poiting at.
  fprintf(stderr, "%p == %p\n", c + 1, &c[1]);

  fprintf(stderr, "\n\n");
  fprintf(stderr, "%s\n", "Nailing pointer arithmetic");
  fprintf(stderr, "%s\n", "==========================");
  // Now let's do something crazy. Let's use an integer pointer to
  // iterate over a character array!
  int *ptr = (int *)c;
  fprintf(stderr, "Item at %p = %c\n", ptr, *ptr);
  ptr++;
  fprintf(stderr, "Item at %p = %c\n", ptr, *ptr);

  // See how the pointer moved 4 bytes because we used an integer pointer
  // to do the arithmetic ?

  return 0;
}