The document details the implementation of a lexical analyzer in a compiler engineering lab, focusing on identifying keywords and identifiers. It discusses the structure and constraints of the token buffer and the necessary definitions for operators and values. The document also includes information on classification functions such as isalpha() and isalnum(), as well as the importance of handling case sensitivity.

1. University of Dammam
Girls’ College of Science
Department of Computer Science
Compiler Engineering Lab
COMPILER
ENGINEERING
LAB # 2 : LEXICAL ANALYZER (CONT.)

2. • Identifiers
• Keywords
• Relational
A LANGUAGE
FOR
Operators
SPECIFYING • Arithmetic
LEXICAL
ANALYZER
Operators
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Compiler Engineering Lab

3. IDENTIFIERS & KEYWORDS
• if the first character isalpha..
• It might be keyword or identifier .
• First you have to check if it is keyword , if it
is not it is going to be an identifier.
• use (strcmp) to compare the string in array
with key words.
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4. IDENTIFIERS & KEYWORDS
• If the lexeme is keyword return the value
of the keyword
• Store each character in array for both
regular identifier and keywords
• Define an array call it (lexbuf) to store the
characters of IDs’ and keywords
• An identifier should be..
{alpha}({alpha}|{digit}|[ _ ])* <= BSIZE
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5. • Analyzer can not process
when the buffer is full,
parser can not process
when the buffer is empty
• the interaction between
TOKEN BUFFER
the two constrained by the
lexical analyzer size of the buffer
and the parser
form a producer – • Buffer hold just one token
consumer pair • Interaction can be
implemented by making
the lexical analyzer a
procedure called by the
parser
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6. • Define these Manifest
Constants :
• BSIZE 128
MANIFEST
CONSTANT • EOF ‘0’
• NONE - 1
• NUM 256
• ID 257
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7. Use these definitions:
IF 310
THEN 320
KEYWORDS
(TOKENS & ELSE 330
VALUES) RELOP 300
* Be careful with case-
sensitive lexemes.
AROP 250
ASS 253
SUM 254
SUB 255
MUL 259
DIV 258
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8. RELOP ( RELATION OPERATIONS )
• Read one character if it matches one of
the RELOP, read one more …
• Declare a char array call it (tvl) [2] to store
the RELOP value
• Use (strcpy) to copy values and (strcmp)
to compare values.
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9. • Relational Operators:
>= , > , == , <=
, > , !=
OPERATORS
TOKEN RELOP
Token Value
GE , GT , EQ, LE ,LT ,NE
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10. • Arithmetic Operators:
= , + , - ,* , /
OPERATORS TOKEN
AROP
Token Value
ASS , SUM , SUB , MUL ,
DIV
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11. ISALPHA()()
# include <ctype.h>
Description
• Classifies an alphabetical character.
• isalpha is a macro that classifies ASCII-
coded integer values by table lookup. For
the default C locale, c is a letter (A to Z or
a to z).
Return Value:
isalpha returns nonzero if c is a letter.
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Compiler Engineering Lab

12. ISALNUM( )
# include <ctype.h>
Description
• Tests for an alphanumeric character.
• isalnum is a macro that classifies ASCII-
coded integer values by table lookup. c is
a letter (A to Z or a to z) or a digit (0 to 9).
Return Value:
• isalnum returns nonzero if c is a letter or
a digit.
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13. QUESTIONS?
Thank you for listening 
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Compiler Engineering Lab