Implementing of switch state-machine

switch (state)
    {
    case a:
      HAL_ADC_Start(&hadc1);
      HAL_ADC_PollForConversion(&hadc1, 1);
      raw = HAL_ADC_GetValue(&hadc1);
      raw_to_volt = (raw * 3.3) / 4095;
      HAL_ADC_Stop(&hadc1);

      sprintf(msg, "(%lu) Hall sensor:  %.4f [V]\r\n", HAL_GetTick()/100, raw_to_volt);
      HAL_UART_Transmit(&hlpuart1, (uint8_t*)msg, strlen(msg), 10);
      flag_sensor = 0;

      break;

    case b:
      /* reading tension and checking the value */
      break;

    case c:
      /* danger state code */
      break;

    case d:
      /* waiting state code */
      break;

    default:
      break;
    }