identifier state is undefined issue

[young umbra]

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[winter vector]

this isn't python, you need to enclose scopes with {}

indentations have "no meaning"

and characters are single quotes

and you need semicolons to end statements

and you're missing a bunch of assignment operators

#include <iostream>
#include <string>

using namespace std;

//(TT + G)* (A + T)

bool DFA(string S) {
  int x = 0;
  int yes = false;
  char state = 'S';

  for (auto x : S) {
    if (state == 'S') {
      if (x == 'T')
        state = '1';
      else
        state = '2';
    }

    if (state = '2') {
      if (x == 'T')
        state = '1';
      else
        state = '3';
    }

    if (state == '2') {
      if (x == 'T')
        state == '3';
      else
        state = '2';
    }

    if (state == '3') {
      if (x == 'a' or x == 'b') state == '3';
    }
  }

  if (state == '1' or state == '2') {
    yes = true;
    return yes;
  }
}

to iterate over some container, you can use the for (auto x : S) { syntax, where x is an element (char) of S (string)

[young umbra]

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