How to execute functions simultaneously in this case?

Projects Programming
17

@gcjr thank you for your reply, I am not using any library for the stepper.

Here is the step function:

void OneStep(bool dir)
{
  if (dir)
  {
    switch (step_number)
    {
    case 0:
      digitalWrite(STEPPER_PIN_1, HIGH);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, LOW);
      break;
    case 1:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, HIGH);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, LOW);
      break;
    case 2:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, HIGH);
      digitalWrite(STEPPER_PIN_4, LOW);
      break;
    case 3:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, HIGH);
      break;
    }
  }
  else
  {
    switch (step_number)
    {
    case 0:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, HIGH);
      break;
    case 1:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, HIGH);
      digitalWrite(STEPPER_PIN_4, LOW);
      break;
    case 2:
      digitalWrite(STEPPER_PIN_1, LOW);
      digitalWrite(STEPPER_PIN_2, HIGH);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, LOW);
      break;
    case 3:
      digitalWrite(STEPPER_PIN_1, HIGH);
      digitalWrite(STEPPER_PIN_2, LOW);
      digitalWrite(STEPPER_PIN_3, LOW);
      digitalWrite(STEPPER_PIN_4, LOW);
    }
  }
  step_number++;
  if (step_number > 3)
  {
    step_number = 0;
  }
}

and I basically loop it how many times I need it, which most likely isn't the best way of doing it. Is there a good library that could replace that?