#include <stdio.h>

int main()
{
   int * ptr;			// a pointer

   printf("The value of ptr = %p\n", ptr);
   printf("Now initializing ptr to null pointer\n");

   ptr = 0;

   printf("The value of ptr = %p\n", ptr);

   if (ptr == 0)
     printf("Pointer unsafe to de-reference\n");
   else
     printf("Pointer safe to de-reference\n");

   printf("Attempting to dereference ptr\n");
   printf("*ptr = %d\n", *ptr);

   return 0;
}