long long b = 5*1024*1024*1024; // 5 gigs, small enough for 64 bits
printf ("%lu\n",sizeof(long long)); // prints 8 (bytes) = 64 bits
warning: integer overflow in expression [-Woverflow]
Because the numbers on the right hand side are of type
long long, so
int arithmetic is performed in the expression, leading to an overflow.
If you add
LL to one of them, it'll promote them all.