Program To Calculate Mathematical Expressions > Lex and Yacc Program

Program To Calculate Mathematical Expressions > Lex and Yacc Program 

System Programming and Compiler Construction

Programs:

pratspcc3.l:

%{

  #include "y.tab.h"

  extern int yylval;

%}

%%

[\t]+        ;

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

\n             {return 0;}

.                {return (yytext[0]);}

%%

int yywrap()

{

   return 1;

}

spcc3.y:

%{

#include<stdio.h>

#include<stdio.h>

%}

%Start S

%token num

%left '+''-'

%left '*''/'

%%

S:E {printf("RESULT = %d\n",$1);

}

;

E:E'+'E {$$=$1+$3;}

 |E'-'E {$$=$1-$3;}

 |E'*'E {$$=$1*$3;}

 |E'/'E {$$=$1/$3;}

 |num {$$=$1;}

%%

main(){

printf("ENTER THE EXPRESSION");

yyparse();

}

int yyerror()

{

return (1);

}

OUTPUT:

[root@localhost ~]# cd Desktop

[root@localhost Desktop]# yacc -d spcc3.y

[root@localhost Desktop]# lex pratspcc3.l

[root@localhost Desktop]# cc -o out3 lex.yy.c y.tab.c -ll

[root@localhost Desktop]# ./out3

ENTER THE EXPRESSION5+4-1

RESULT = 8

[root@localhost Desktop]# ./out3

ENTER THE EXPRESSION6/2+7

RESULT = 10