Use the typedef keyword to define an abbreviated name, or
   synonym,  for a lengthy type definition.  Grammatically,
   typedef is a storage-class specifier, so it can precede any valid
   declaration.  In  such  a declaration, the identifiers name types
   instead of variables. For  example:

       typedef char CH, *CP, STRING[10], CF();

   In the scope of this declaration, CH is a synonym for "character,"
   CP  for "pointer to character," STRING for "10-element array of
   characters," and CF for "function returning a character." Each of
   the  type definitions can be used in that scope to declare
   variables. For example:

       CF     c;       /* c IS A FUNCTION RETURNING A CHARACTER */
       STRING s;       /* s IS A 10-CHARACTER STRING            */