ARRAY
- all elements are the same type
- elements don't have distinct roles.  array[0] is the first,  array[1] is the second, and so on.

STRUCT
- fields can be different types
- fields have different names to reflect their roles


TYPEDEF
- Basic syntax:
  typedef  «TYPE»    «NAME»
- Example:
  typedef int Number;
  // type is 'int'
  // name is 'Number'
- Example:
  typedef struct { int x; int y; } Point;
  // type is 'struct { int x; int y; }'
  // name is 'Point'
- With struct types:
  typedef struct {
    «DECLARATION»;
    «DECLARATION»;
  } «NAME»;

STRUCT vs UNION
- Struct stores all fields.
- Union stores only one field at a time (to save space).