String Reverse Using pointers

I have written a code to reverse the string . It is not working . Is my logic right? How to make it work . I wish to make this one work . I have written using some other logic and it is working . I wish to know how to fix this logic.

#include "stdafx.h"


int _tmain(int argc, _TCHAR* argv[])
{
    char *a="This is Anfield"; //Char string
    char *b;  // Reverse string to be copied here
    int count=0; // Count the length of string
    while(*a!='\0')
    {
        count++;
        a++;
    }
    int len=count+1; // Length of string
    int i,j;
    i=j=0;
    for(i=count;i>=0;i--)
    {
        *(a+count)=*(b+j); //Tail of string will be copied to beginning
        j++;
    }
    printf("\n%s",*b);// Print Reversed String
    return 0;
}

There is some run time error in "char *b" Line..

Tags: C++, C