const int BTN_PIN = 4;
const int RED_LED_PIN = 2;
const int YEL_LED_PIN = 3;

int counter = 0;
int oldCount = -1;
int oldBtnVal = 1; // INPUT_PULLUP, pin idles HIGH

int checkButton()  {
  int buttonValue = digitalRead(BTN_PIN);
  if (buttonValue != oldBtnVal) {   // button changed
    oldBtnVal = buttonValue;        // remember state
    if (buttonValue == LOW) {       // was just pressed
      //Serial.println("Button pressed");
      counter++;
      if (counter > 3) counter = 0;
    } else {
      //Serial.println("Button released"); // was just released
    }
    delay(20);  // short delay to debounce button
  }
  return counter;
}

void setup() {
  Serial.begin(9600);
  pinMode(BTN_PIN, INPUT_PULLUP);
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(YEL_LED_PIN, OUTPUT);
}

void loop() {
  int count = checkButton();
  if (count != oldCount)  {
    oldCount = count;
    if (count == 0) {
      digitalWrite(RED_LED_PIN, LOW);
      digitalWrite(YEL_LED_PIN, LOW);
    }
    if (count == 1) {
      digitalWrite(RED_LED_PIN, HIGH);
      digitalWrite(YEL_LED_PIN, LOW);
    }
    if (count == 2) {
      digitalWrite(RED_LED_PIN, LOW);
      digitalWrite(YEL_LED_PIN, HIGH);
    }
    if (count == 3) {
      digitalWrite(RED_LED_PIN, HIGH);
      digitalWrite(YEL_LED_PIN, HIGH);
    }
    Serial.print("Count = ");
    Serial.print(count);
    Serial.print("\tYellow LED: ");
    Serial.print(digitalRead(YEL_LED_PIN) ? "on " : "off");
    Serial.print("\t\tRed LED: ");
    Serial.println(digitalRead(RED_LED_PIN) ? "on " : "off");
  }
}