DFA Implement of (A|B)*ABB

#include <stdio.h>
#define TOTAL_STATES 4
#define FINAL_STATES 1
#define ALPHABET_CHARCTERS 2
#define UNKNOWN_SYMBOL_ERR 0
#define NOT_REACHED_FINAL_STATE 1
#define REACHED_FINAL_STATE 2
enum DFA_STATES {q0,q1, q2, q3};
enum input {a,b};

int Accepted_states[FINAL_STATES]= {q3};
char alphabet[ALPHABET_CHARCTERS]= {'a','b'};
int Transition_Table[TOTAL_STATES][ALPHABET_CHARCTERS];
int Current_state=q0;

void DefineDFA()
{
Transition_Table[q0][a] = q1;
Transition_Table[q0][b] = q0;
Transition_Table[q1][a] = q1;
Transition_Table[q1][b] = q2;
Transition_Table[q2][a] = q1;
Transition_Table[q2][b] = q3;
Transition_Table[q3][a] = q0;
Transition_Table[q3][b] = q1;
}

int DFA(char current_symbol)
{
int i,pos;
for(pos=0; pos<ALPHABET_CHARCTERS; pos++)
if(current_symbol==alphabet[pos])
break;//stops if any character other than a or b
if(pos==ALPHABET_CHARCTERS)
return UNKNOWN_SYMBOL_ERR;
for(i=0; i<FINAL_STATES; i++)
if((Current_state=Transition_Table[Current_state][pos])==Accepted_states[i])
return REACHED_FINAL_STATE;
return NOT_REACHED_FINAL_STATE;
}

int main(void)
{
char current_symbol;
int result;

DefineDFA();    //Fill transition table

printf("Enter a string with 'a' s and 'b's:\nPress Enter Key to stop\n");


while((current_symbol=getchar())!= '\n')
if((result= DFA(current_symbol))==UNKNOWN_SYMBOL_ERR)
break;
switch (result)
{
case UNKNOWN_SYMBOL_ERR:
printf("Unknown Symbol %c",current_symbol);
break;
case NOT_REACHED_FINAL_STATE:
printf("Not accepted");
break;
case REACHED_FINAL_STATE:
printf("Accepted");
break;
default:
printf("Unknown Error");
}
printf("\n\n\n");
return 0;
}