TinyOS

Hello, I am new to tinyos and nesc. and I have the following data strucuture

typedef nx_struct rt_link {
nx_addr_t target;
nx_addr_t nexthop;
} rt_link_t;

typedef struct rt_entry {
double some_double;
uint8_t some_int;
} rt_entry_t;

uint8_t flag = 0x01;
uint8_t i=0;
rt_link_t * buf;
rt_entry_t table[10];

if ( flag & 0x01)
{
buf[i].target = table[i].some_double;
buf[i].nexthop = table[i].some_int;
}

and if I use
if ( flag == 1)
{
buf[i].target = table[i].some_double;
buf[i].nexthop = table[i].some_int;
}

I will get different value from buf[0], whats the difference?