CALC.L 
%{ 
#include<stdio.h>
#include<stdlib.h>
void yyerror(char *);
#include "y.tab.h" 
int yylval; 
%} 
%% 
[a-z] {yylval=*yytext='&'; return VARIABLE;} 
[0-9]+ {yylval=atoi(yytext); return INTEGER;} 
CALC.Y 
[\t] ; 
%% 
int yywrap(void) 
{ 
return 1; 
} 
%token INTEGER VARIABLE 
%left '+' '-' 
%left '*' '/' 
%{ 
int yylex(void); 
void yyerror(char *); 
int sym[26]; 
%} 
%% 
PROG: 
PROG STMT '\n' 
; 
STMT: EXPR {printf("\n %d",$1);} 
| VARIABLE '=' EXPR {sym[$1] = $3;} 
; 
EXPR: INTEGER 
| VARIABLE {$$ = sym[$1];} 
| EXPR '+' EXPR {$$ = $1 + $3;} 
| '(' EXPR ')' {$$ = $2;} 
%%
void yyerror(char *s) 
{ 
printf("\n %s",s); 
return; 
} 
int main(void) 
{ 
printf("\n Enter the Expression:"); 
yyparse(); 
return 0; 
 
 

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