if-else with lex, yacc (ToDo: Add support for nested if-else)

pgm.l

%{
  #include "y.tab.h"
%}
%%
"if" {return IF;}
"else" {return ELSE;}
"&&" {return AND;}
"||" {return OR;}
"<=" {return LE;}
">=" {return GE;}
"==" {return EQ;}
"<" {return LT;}
">" {return GT;}
"!=" {return NE;}
[a-z]+ {return alpha;}
[0-9]+ {return num;}
[\t] ;
[\n] {return 0;}
. {return yytext[0];}
%%
int yywrap()
{
  return 1;
}

pgm.y

%{
    #include <stdio.h>
    int yylex();
    void yyerror();
%}
%token num alpha LT GT EQ LE GE NE AND OR
%left '+''-'
%left '*''/'
%right '^'
%right '='
%nonassoc UMINUS
%nonassoc IF
%nonassoc ELSE
%left GE NE LT GT LE EQ
%left AND OR
%%
S:ST {printf("ACCEPTED\n");}
ST:IF'('F')''{'ST'}' %prec IF
  |IF '('F')''{'ST'}'ELSE'('ST')'
  |E';'
F:C LO C
  |C
LO:AND
  |OR
C:E RELOP E
E:alpha'='E
  |E'+'E
  |E'-'E
  |E'*'E
  |E'/'E
  |E'^'E
  |'-'E %prec UMINUS
  |alpha
  |num
RELOP:LT
  |GT
  |EQ
  |LE
  |GE
  |NE
  ;
%%
void yyerror (char const *s) {
  fprintf (stderr, "%s\n", s);
}
#include <stdio.h>
int main(){
  printf("Enter the expression\n");
  yyparse();
  return 0;
}