Identifier

Definition: Name of Variables, Labels, Functions, Parameters

Syntax Considerations

• Maximum Length: Affects Readability
  • Early Basic: 2 characters

    Dim c3 As Integer
    Dim p0 As Double
    

  • FORTRAN 77: 6 characters

    REAL INTERE,PRINCI
    

  • COBOL: 30 characters
  • ANSI C/C++: 31 characters
  • Ada: Any length
• Connector Character
  • C++: Underscore

    int interest_rate;
    char middle_initial;
    

  • LISP: Hyphen

    (defun function( old-list new-list )
      ... )
    

  • Pascal, Modula-2, FORTRAN 77: None
• Case Sensitivity (C++, Pascal, Modula-2)
  • Readability Impaired?
  • Writability: Modula-2

    FROM InOut IMPORT WriteInt, WriteString, ReadInt, WriteLn;
    

• Special Words
  • Reserved Words: Not usable as identifiers
    • COBOL, Pascal, C++
    • Disadvantage: If language is extended, old programs may not compile
  • KeyWords: Usable as identifiers, Special only in context
    • FORTRAN

            INTEGER REAL
            REAL = 5
          

    • Disadvantage: Readability impaired
  • ALGOL 60: Reserved Words in a different font!

Symbol Table: Identifier -> (Address, Offset)