Basic Pascal Tutorial/Chapter 1/Identifiers
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.
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