Notes

#include <stdio.h>
#include<conio.h>
#define TOTAL_STATES 2
#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};
enum input{a,b};
int Accepted_states[FINAL_STATES]={q1};
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] = q0;
}
int DFA(char current_symbol)
{
int i,j;
for(j=0;j<ALPHABET_CHARCTERS; j++)
if(current_symbol==alphabet[j])
break;
if(j==ALPHABET_CHARCTERS)
return UNKNOWN_SYMBOL_ERR;
for(i=0;i<FINAL_STATES;i++)
if((Current_state=Transition_Table[Current_state][j])==Accepted_states[i])
return REACHED_FINAL_STATE;
return NOT_REACHED_FINAL_STATE;
}
int main(void)
{
char current_symbol;
int result;

DefineDFA();
printf("Enter a string with 'a' s and 'b's:n Press Enter Key to stopn");

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("nnn");
getch();
return 0;
}