unit III


pls click here unit 3

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operator precendence parsing

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Operator Precedence Parsing ·           The grammars that have the property that no production right side is ε or has two adjacent nonterminals. ·           A grammar with the later property is called an operator grammar. ·           The following grammar for expressions is  not  an operator grammar: E → E A E | ( E ) | - E | id A → + | - | * | / | ^                                         o     Because the right side EAE has two consecutive nonterminals. ·           To obtain the (Grammar 2.9.1) as operator grammar, substitute for A each of its alternatives for production E.                ...
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program1-----> To count the no of tokens and display to the token

%{  #include<stdio.h> #include<string.h> int n = 0 ;  %}    %%  "while"|"if"|"else" {n++;printf("\t keywords : %s", yytext);}    "int"|"float" {n++;printf("\t keywords : %s", yytext);}      [a-zA-Z_][a-zA-Z0-9_]* {n++;printf("\t identifier : %s", yytext);}    "<="|"=="|"="|"++"|"-"|"*"|"+" {n++;printf("\t operator : %s", yytext);}   [(){}|, ;]    {n++;printf("\t separator : %s", yytext);}    [0-9]*"."[0-9]+ {n++;printf("\t float : %s", yytext);}    [0-9]+ {n++;printf("\t integer : %s", yytext);}  "\n"  {printf("\n total no. of token = %d\n", n);}  %%       int yywrap(void){} int main()    {      yylex();     printf("check");               return 0;       } 
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lab record

EX.NO.1      STUDY OF LEX TOOL AIM : To study about lexical analyser generator [LEX TOOL]. 1.Introduction: The unix utility lex parses a file of characters. It uses regular expression matching; typically it is used to ‘tokenize’ the contents of the file. In that context, it is often used together with the yacc utility. 2 Structure of a lex file A lex file looks like ...definitions... %% ...rules... %% ...code... Here is a simple example: %{ int charcount=0,linecount=0; %} %% . charcount++; \n {linecount++; charcount++;} %% int main() { yylex(); printf("There were %d characters in %d lines\n", charcount,linecount); return 0; } 2.1 Block Diagram : LEX COMPILER   LEX PGM----- à                               ...
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