Basic Pascal Tutorial/Chapter 1/Identifiers

From Lazarus wiki
Revision as of 20:05, 25 November 2007 by Kees (talk | contribs) (New page: 1B - Identifiers (author: Tao Yue, state: unchanged) Identifiers are names that allow you to reference stored values, such as variables and constants. Also, every program must be identifi...)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigationJump to search

1B - Identifiers (author: Tao Yue, state: unchanged)

Identifiers are names that allow you to reference stored values, such as variables and constants. Also, every program must be identified (get it?) by an identifier.

Rules for identifiers:

  • Must begin with a letter from the English alphabet.
  • Can be followed by alphanumeric characters (alphabetic characters and numerals), or the underscore (_).
  • May not contain special characters, such as:
 ~ ! @ # $ % ^ & * ( ) _ + ` - = { } [ ] : " ; ' < > ? , . / | \

Several identifiers are reserved in Pascal -- you cannot use them as your own identifiers. They are:

and array begin case const div do downto
else end file for forward function goto if
in label mod nil not of or packed
procedure program record repeat set then to type
until var while with

Also, Pascal has several pre-defined identifiers. You can replace them with your own definitions, but then you'd be deleting part of the functionality of Pascal.

abs arctan boolean char cos dispose eof eoln
exp false input integer ln maxint new odd
ord output pack page pred read readln real
reset rewrite round sin sqr sqrt succ text
true trunc write writeln

Pascal is not case sensitive! MyProgram, MYPROGRAM, and mYpRoGrAm are equivalent. But for readability purposes, it is a good idea to use meaningful capitalization!

Identifiers can be any length, but many Pascal compilers will only look at the first 32 characters or so. That is,

    ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFAlphaBeta
    ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGammaDelta

may be equivalent to some Pascal compilers because the differences begin in the 33rd character.

To make your code compilable by all compilers, use a reasonable length for identifiers -- up to 15 characters. That way, you'll also save on typing.

previous contents next