a weird result when I try to print the value of point by %p format

it's really ridiculous when I try to test my code today

I had never known there are some key word or syntax about  "nil"  in C/C++, to make it clear I duplicate it in the following test code:

/* nil.c by vinco at 2011-08-03
* os : ubuntu 9.10
* compiler :CC/GCC
*/
#include<stdio.h>

int main()
{
        char* p = NULL;
        printf("\n");
        printf("p = %p\n",p);
        printf("p = %s\n",p);
        printf("\n");
        return 0;
}

compile and run it:

root@vinco:/home/vinco# make nil
cc     nil.c   -o nil
root@vinco:/home/vinco# ./nil 

p = (nil)
p = (null)

root@vinco:/home/vinco# 

I search it in Google and Baidu, it's seem that "nil"  is same with NULL to some extent , means no value.

does that the truth ?

I would  appreciate it if you could explain it clearly for me !!!