8. Is NULL always defined as 0?

Ans:
NULL is defined as either 0 or (void*)0. These values are almost identical; either a literal zero or a void pointer is converted automatically to any kind of pointer, as necessary, whenever a pointer is needed (although the compiler can’t always tell when a pointer is needed).

Ex - 1:  What is the output?
main()
{
                        int a=2,*f1,*f2;
            f1=f2=&a;
                        *f2+=*f2+=a+=2.5;
            printf("\n%d %d %d",a,*f1,*f2);
}

Ans:
16 16 16

Ex - 2 what is the output?:

main()
{
            static int a[3][3]={1,2,3,4,5,6,7,8,9};
            int i,j;
            static *p[]={a,a+1,a+2};
                        for(i=0;i<3;i++)
            {
                                    for(j=0;j<3;j++)
 
                                   printf("%d\t%d\t%d\t%d\n",*(*(p+i)+j),
                                    *(*(j+p)+i),*(*(i+p)+j),*(*(p+j)+i));
                        }
}

Ans:
                                    1       1       1       1
                                    2       4       2       4
                                    3       7       3       7
                                    4       2       4       2
                                    5       5       5       5
                                    6       8       6       8
                                    7       3       7       3
                                    8       6       8       6
                                    9       9       9       9
Explanation:
                        *(*(p+i)+j) is equivalent to p[i][j].