Basic Pascal Tutorial/Chapter 1/Identifiers/bg

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Идентификатори

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

Идентификаторите са имена, които ви позволяват да се позовавате на съхранени стойности, като променливи и константи. Също така, всяка програма трябва да бъде идентифицирана (схванахте ли?) с идентификатор.

Правила за идентификаторите:

• Трябва да започва с латинска буква (a..z или A..Z, Pascal не различава големи от малки букви) от или долна черта (_).
• Може да бъде последвано от още букви (a..z, A..Z), цифри (0..9) или долни черти (_), във всякаква комбинация.
• Не може да бъде резервирана дума като например begin, for, case, absolute и др.
• Не може да съдържа специални символи, като:

  ~! @ # $% ^ & * () + `- = {} []:"; '<>?,. / | \ (или интервал) 

Запазени думи

В Pascal някои идентификатори са запазени и не можете да ги използвате като свои собствени такива. Според FPC справочник те са групирани така:

• Запазени думи от Turbo Pascal
• Запазени думи от Delphi
• Запазени думи от Free Pascal

Запазени думи от Turbo Pascal

absolute	and	array	asm	begin	break	case	const
constructor	continue	destructor	div	do	downto	else	end
file	for	function	goto	if	implementation	in	inherited
inline	interface	label	mod	nil	not	object	of
on	operator	or	packed	procedure	program	record	reintroduce
repeat	self	set	shl	shr	string	then	to
type	unit	until	uses	var	while	with	xor

Запазени думи от Delphi

Запазените думи от Delphi (II) са същите като тези от Turbo Pascal, плюс следните:

as	class	except	exports	finalization	finally	initialization
is	library	on	property	raise	threadvar	try

Запазени думи от Free Pascal

В допълнение към запазените думи от Turbo Pascal и Delphi, Free Pascal запазва още и следните:

dispose

exit

false

new

true

break

continue

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!

There are two possible methods you could choose to apply to your identifiers: CamelCase and underscore as space. CamelCase, as it appears, means that separate words in an identifier are capitalized, so that you have newPerson or NewPerson instead of newperson. Using underscore as space means you separate words in an identifier with underscores, so that you have new_person instead of newperson. Or you could combine the two, so that you have new_Person or New_Person instead of newperson.

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. Free Pascal limits identifiers to 127 characters.

This is extremely generous. The original Pascal compiler for the CDC 6000 mainframe only noticed the first 10 characters of an identifier. This was because the CDC had a 60 bit word, and by using 6 bit characters (all upper case letters plus digits and some punctuation) an identifier could fit in one word. You could have more than 10 characters in an identifier, but only the first 10 counted, so ThisIsObviouslyAVeryLongNamw and ThisIsObviouslyAnEvenLongerName would be considered the same.

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.

While it is a good idea to make identifiers to be mnemonic with the use of longer names, there is nothing wrong with using very short identifiers in specific uses. it is extremely common to use I, J, and K< as the control variable in a for loop.