This example shows how the base type of a pointer is
used by the compiler.

1.  Some of its usual type checking is affected by the base
    type of the pointer.  *p has the base type of p.  p is
    a pointer to a base type value, and int* and float* are
    not the same type.

2.  The value of p+3 depends on the base type of p.  In particular,
    the implementation of pointers are that they have the address
    of a byte.  If p is an int*, that means p+3 is 12 larger than
    p (since each int is 4 bytes).  If p is a double*, p+3 is 
    24 larger than p (because a double is 8 bytes).

(It also shows that the symbol "main" is a pointer.)