Char pointer problem

[gaurav_13191]

I found the following code on internet for adding two numbers using pointers:-

#include<stdio.h>
	int main()
	{
	 int a=30000,b=20,sum;
	 char *p;

         p=(char *)a;
	 sum= (int)&p[b];
	 printf("%d",sum);
	 return 0;

	 }

But I can't understand how p holds the value 30000 or how the result of the program is addition of 30000 and 20..

And another small question.. What does the following statement declare:

char *a[][40];

What does '40' signify in this? Please help me out!!

[Narue]

>But I can't understand how p holds the value 30000 or how the result of the program is addition of 30000 and 20..
Presumably this hideous trick is meant to add two numbers without using the + operator. a is converted to a pointer to char, thus making the address pointed to by be 30000. Then the subscript operator is used to get to an object at an offset of b beyond the address pointed to by p. b is 20 and p+140==30020 (p is a pointer to char so that the step size is 1 rather than sizeof(int)). Use the address-of operator on the resulting object, convert the address back to int, and you've got the effect of a+b.

>What does the following statement declare: [ char *a[][40]; ]
Break it down from the inside out:

a       // a is an
       []     // array of undefined size of
         [40] // arrays of 40
     *        // pointers to
char          // char