Parser for sample language using YACC

Lex File

%{

            #include<stdio.h>

            #include"y.tab.h"

            int line=0;

%}

%%

[ \t]+                            ;

int|float|char                  return DT;

main                             return MAIN;

return                           return RET;

if|for|while|else  return KEYW;

[a-zA-Z][a-zA-Z0-9]* return ID;

[0-9]+                          return NUM;   

[(){},;=]                       return yytext[0];

\n                                 line++;

[><>=<===]                return AOP;

%%

yywrap()

{

return 1;

}

Yacc File

%{

            #include<stdio.h>

            extern FILE *yyin;

            extern int line;

%}

%token DT NUM ID RET MAIN KEYW AOP

%%

Pdash:P                        {printf("\n Parsing Done....No Syntax Error");}

P:DT MAIN '(' ')' '{' S R '}'

S:DS S

 |ES S

 |CS S

 |

DS:DT V ';'

V:ID|V','ID

ES:ID'='E';'

E:NUM|ID

CS:KEYW '(' A ')' '{' S '}'

A:ID AOP ID|ID AOP NUM|';'';'

R :RET NUM';'

%%

int main()

{

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

            yyparse();

}

yyerror()

{

            printf("\n Error at line no:%d",line);

}

Input text file

int main()

{

            int a,b,c;

            b=4;

            a=b;

            if(a>2)

            {

            for(;;)

            {

                        c=2;

            }

            }

            return 0;

}

Output

student@ubuntu:~$ yacc -d parse.y

student@ubuntu:~$ lex lex1.l

student@ubuntu:~$ cc y.tab.c lex.yy.c

student@ubuntu:~$ ./a.out

Parsing Done....No Syntax Error

student@ubuntu:~$