pgm12.y

%{
	#include <stdio.h>
	#include <ctype.h>
	#include <stdlib.h>
	#include <string.h>
	#define MAX 100
	int getREindex(const char*);
	signed char productions[MAX][MAX];
	int count =0,i,j;
	char temp[MAX+MAX],temp2[MAX+MAX];
%}
%token ALPHABET
%left '|'
%left '.'
%nonassoc '*''+'
%%
S: re '\n' {
		printf("This is RMD\n");
		for(i=count-1;i>=0;--i)
		{
			if(i==count-1)
			{
				printf("\nre=>");
				strcpy(temp,productions[i]);
				printf("%s",productions[i]);
			}
			else
			{
				printf("\n=>");
				j=getREindex(temp);
				temp[j]='\0';
				sprintf(temp2,"%s%s%s",temp,productions[i],(temp+j+2));
				printf("%s",temp2);
				strcpy(temp,temp2);
			}
		}
		printf("\n");
		exit(0);
	   }
re: ALPHABET  {
		temp[0]=yylval;
		temp[1]='\0';
		strcpy(productions[count++],temp);
	    }
   | '('re')' { strcpy(productions[count++],"(re)");}
   | re'*' { strcpy(productions[count++],"re*");}
   | re'+' { strcpy(productions[count++],"re+");}
   | re'|'re { strcpy(productions[count++],"re|re");}
   | re'.'re { strcpy(productions[count++],"re.re");}
   ;
%%
int main( int argc, char** argv)
{
	yyparse();
	return 0;
}
yylex()
{
	signed char ch=getchar();
	yylval=ch;
	if(isalpha(ch))
	return ALPHA;
	return ch;
}
yyerror()
{
	fprintf(stderr,"INVALID REGEXP\n");
	exit(0);
}
int getREindex(const char *str)
{
	int i=strlen(str)-1;
	for(;i>=0;--i)
	{
		if(str[i]=='e' && str[i-1]=='r')
		return i-1;
	}
}