Description

Phases Of Compilation Lexical Analyzer
Assignment
Phases Of Compilation

Lexical Analyzer
I converts the input program into a sequence of Tokens.
I can be implemented with the help of Finite Automata.
Lexical Analyzer

Programmer‘s View

Loop and switch Approach
/* Single caharacter lexemes */
#define LPAREN_TOK ’(’
#define GT_TOK ’>’
#define RPAREN_TOK ’)’
#define EQ_TOK ’=’
#define MINUS_TOK ’-’
#define SEMICOLON_TOK ’;’ /*………………..
…………………..*/
/* Reserved words */
#define WHILE_TOK 256
/*………………..
…………………..*/
/* Identifier, constants..*/
#define ID_TOK 350
#define INTCONST 351
/*………………..
…………………..*/
Based on the Concept of Deterministic finite Automata
Transition Diagram for >=

Transition Diagrams for Relational Operators

Transition Diagrams for Identifiers or Keywords

Transition Diagrams for White spaces

Implementing a Transition Diagram
int yylex(){
while(1){
switch(state){
case 0: c = nextchar(); if (c== blank || c== tab || c==newline){ state = 0;
}
else if (c == ’<’) state = 1; else if (c == ’=’) state = 5; else if (c == ’>’) state = 6; else state = fail(); break; } case 1:
.
.
case 9: c = nextchar(); if (isletter(c))state = 10; else state = fail(); break;
case 10: c = nextchar(); if (isletter(c)) state = 10; else if (isdigit(c)) state = 10; else state = 11; break;
}
}

Assignment
Implement a lexical analyzer for the following types of tokens:
I Arithmetic, Relational, Logical, Bitwise and Assignment Operators of C.
I Reserved words: int, float, char, for, while, if and else I Identifier.
I Integer Constants.
I Parentheses, Curly braces
Follow the ideas of transition diagram, yytext, yyleng, etc as stated in the study material.