lex yacc program to add and subtract two numbers

lex.l file

%{

#include<stdio.h>

#include "y.tab.h"

extern int yylval;

%}

%%

[0-9]+ {yylval= atoi(yytext);return num;}

[+-] {return yytext[0];}

[ \t]+ ;

\n {return 0;}

%%

yacc.y file

%{

     #include<stdio.h>

%}

%token num

%%

sta: exp { printf("%d",$1);}

exp: num '+' num {$$=$1 + $3;}

    | num '-' num {$$=$1 - $3;}

     ;

%%

main()

{

   yyparse();

}

yyerror(char *s)

{

  printf("errror:%s",s);

}

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