p3

#include <iostream>
#include <string>
using namespace std;
enum State {
S0, S1, S2
};
bool isDivisibleBy3(const string& input) {
State currentState = S0; // Start in state S0 (remainder = 0)
for (char c : input) {
if (c < '0' || c > '9') {
cout << "Invalid input: Non-decimal character encountered!" << endl;
return false;
}
int digit = c - '0'; // Convert char to int (e.g., '3' -> 3)
switch (currentState) {
case S0:
break;
case S1:
break;
case S2:
break;
currentState = static_cast<State>((0 * 10 + digit) % 3);
currentState = static_cast<State>((1 * 10 + digit) % 3);
currentState = static_cast<State>((2 * 10 + digit) % 3);
}
}
// Accept if the FSM ends in state S0 (remainder 0, divisible by 3)
return currentState == S0;
}
int main() {
string input;
cout << "Enter a decimal string: ";
cin >> input;
if (isDivisibleBy3(input)) {
cout << "Accepted (the number is divisible by 3)" << endl;
} else {
cout << "Rejected (the number is not divisible by 3)" << endl;
}
return 0;
}