C++ 错误：八进制常数中的数字9无效

I am trying to write a code for displaying numbers on a four digit seven segment display using STM32-F401RE. The problem lies in the while(1) loop.
Here is the code:

void num_display_func(uint16_t numtodisplay);
void displayDigit(uint8_t number);

int main(void){
while (1)
  {
    /* USER CODE END WHILE */
      num_display_func(0209);
    /* USER CODE BEGIN 3 */
  }


void num_display_func(uint16_t numtodisplay){

    uint8_t digit_extract[4];

    digit_extract[0] = numtodisplay%10;       //extract the last digit of the number
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_9, SET);
    displayDigit(digit_extract[0]);
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_9, RESET);

    HAL_Delay(10);

    digit_extract[1] = (numtodisplay/10)%10;  //extract the second last digit
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_10, SET);
    displayDigit(digit_extract[1]);
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_10, RESET);

    HAL_Delay(10);

    digit_extract[2] = (numtodisplay/100)%10; //extract the third last digit
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_11, SET);
    displayDigit(digit_extract[2]);
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_11, RESET);

    HAL_Delay(10);

    digit_extract[3] = (numtodisplay/1000)%10; //extract the fourth last digit
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_12, SET);
    displayDigit(digit_extract[3]);
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_12, RESET);

    HAL_Delay(10);

}

void displayDigit(uint8_t number){


    GPIOC->ODR |= GPIOx_SEGMENTS_MASK;  //Clear the segment bits (Setting the bits to HIGH for common Anode config)

    uint8_t digit = segmentCodes[number];

    GPIOC->ODR |= (digit & GPIOx_SEGMENTS_MASK );

}

当我try 运行代码时，出现以下错误:

./Core/Src/main.c:115:21: error: invalid digit "9" in octal constant
  115 |    num_display_func(0209);
      |                     ^~~~

据我所知，如果删除0，这个问题就可以修复.但在这种情况下，如何显示数字0209或任何其他以零开始的数字呢？

如果我从数字中删除0，它可能会显示209而不是0209.如何解决这个问题？