Typedefs

User defined type names
Provides an "alias" for existing types
typedef  new_type  existing_type;

 typedef  std::string::size_type  str_sz;
 typedef  std::string::difference_type  str_df;
 str_sz  a  =  s.find('a');
 str_sz  e  =  s.find('e');
 str_df  d  =  e  -  a;