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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prg 3&4

Aim: To write a program to implement Ambiguous grammar using YACC and LEX. Grammar: E->E+E | E-E |E*E | E/E|(E)|id Step 1: Start the program. Step 2: Declare yyerror, yylval. Step 3: Include the required header files.                                                                                                                                ...
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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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