boolean condition = true;

void setup() {
  Serial.begin(115200);
}

void loop()
{
  test();
}

void test() {
  static boolean firstEntry = true;
  static boolean callStuffC = false;
  if (firstEntry) {
    firstEntry = false;
    doStuffA();
  }
  if (checkCondition()) {
    doStuffB();
    callStuffC = true;
  } else {

    if (callStuffC) {
      callStuffC = false;
      doStuffC();
    }
    doStuffA();
  }
}

boolean checkCondition() {
  static int count = 0;
  count++;
  if (count > 4) {
    count = 0;
    condition = !condition;
  }
  return condition;
}

void doStuff(char stuffChar) {
  Serial.print("This is stuff");
  Serial.println(stuffChar);
  delay(500);   // This delay only here to reduce the lines/second printed to the serial monitor
}

void doStuffA() {
  doStuff('A');
}

void doStuffB() {
  doStuff('B');
}

void doStuffC() {
  doStuff('C');
}