code generation using LEX and YACC

-----------------------------------LEX FILE--------------------------------------

%{

#include<stdio.h>

#include<string.h>

#include "y.tab.h"

%}

%%

[a-z][a-z0-9]* {strcpy(yylval.var,yytext);return NAME;}

[+]  {strcpy(yylval.var,yytext);return PLUS;}

[=]  {strcpy(yylval.var,yytext);return EQUAL;}

[-] {strcpy(yylval.var,yytext);return SUBT;}

[*] {strcpy(yylval.var,yytext);return MULT;}

[/]    {strcpy(yylval.var,yytext);return DIVI;}

[\n\t] {return yytext[0];}

%%

------------------------------YACC FILE----------------------------------------

%{

#include<stdio.h>

#include<ctype.h>

#include<string.h>

FILE *fout;

%}

%token<var> NAME PLUS EQUAL MULT DIVI SUBT

%type<var> exp

%union

{

char var[10];

}

%right EQUAL

%left PLUS SUNT

%left MULT DIVI

%%    

      

input:line'\n'input

     |'\n'input

     |/*empty*/

     ;

line:NAME EQUAL exp {fprintf(fout,"MOV %s,AX\n",$1);}

    ;

exp:NAME PLUS NAME {fprintf(fout,"MOV AX,%s \n ADD AX,%s\n",$1,$3);}

    |NAME SUBT NAME {fprintf(fout,"MOV AX,%s \n SUB AX,%s\n",$1,$3);}

    |NAME MULT NAME {fprintf(fout,"MOV AX,%s \n MUL AX,%s\n",$1,$3);}

    |NAME DIVI NAME {fprintf(fout,"MOV AX,%s \n DIV AX,%s\n",$1,$3);}

    |NAME      {strcpy($$,$1);}

    ;

%%

extern yylineno;

yyerror()

{

       printf("\neroor %d",yylineno);   

}

yywrap()

{

return 1;

}

extern FILE *yyin;

main()

{

FILE *fin;

fin=fopen("input.txt","r");

fout=fopen("out.txt","w");

yyin=fin;

yyparse();

fcloseall(); 

return 0;

}

------------------------------------INPUT FILE-----------------------

t1=a+b

t2=b+t1

c=t2

--------------------------------OUTPUT FILE---------------------------

MOV AX,a

ADD AX,b

MOV t1,AX

MOV AX,b

ADD AX,t1

MOV t2,AX

MOV c,AX