#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<stdlib.h>

int main() {
  char s[20], c;
  int state = 0, i = 0;

  //clrscr();
  //Enter a String: aaaabbbbb

  printf("\n Enter a string:");
  gets(s);

  while (s[i] != '\0') {
    switch (state) {

    case 0:
      c = s[i++];
      if (c == 'a')
        state = 1;
      else if (c == 'b')
        state = 2;
      else
        state = 6;
      break;

    case 1:
      c = s[i++];
      if (c == 'a')
        state = 3;
      else if (c == 'b')
        state = 4;
      else
        state = 6;
      break;

    case 2:
      c = s[i++];
      if (c == 'a')
        state = 6;
      else if (c == 'b')
        state = 2;
      else
        state = 6;
      break;

    case 3:
      c = s[i++];
      if (c == 'a')
        state = 3;
      else if (c == 'b')
        state = 2;
      else
        state = 6;
      break;

    case 4:
      c = s[i++];
      if (c == 'a')
        state = 6;
      else if (c == 'b')
        state = 5;
      else
        state = 6;
      break;

    case 5:
      c = s[i++];
      if (c == 'a')
        state = 6;
      else if (c == 'b')
        state = 2;
      else
        state = 6;
      break;

    case 6:
      printf("\n %s is not recognised.", s);
      exit(0);
    }
  }

  if (state == 1)
    printf("\n %s is accepted under rule 'a'", s);
  else if ((state == 2) || (state == 4))
    printf("\n %s is accepted under rule 'a*b+'", s);
  else if (state == 5)
    printf("\n %s is accepted under rule 'abb'", s);

  getch();
}