我们将通过Arduino IDE 写一个代码使小机器人可以进行循迹运动。具体表现为：在地面传感器未检测到黑线时直行两边同时感应到黑线时第一次左转 第二次右转第三次左转第四次右转。右转后开始沿墙运动源代码如下帮我改成如上作用的代码改变地方要标注出来

//定义左右电机引脚
int leftMotor = 9;
int rightMotor = 10;

//定义地面传感器引脚
int leftSensor = A0;
int rightSensor = A1;

//定义黑线阈值
int threshold = 500;

void setup() {
  //初始化引脚
  pinMode(leftMotor, OUTPUT);
  pinMode(rightMotor, OUTPUT);
  pinMode(leftSensor, INPUT);
  pinMode(rightSensor, INPUT);
}

void loop() {
  //读取左右传感器数值
  int leftValue = analogRead(leftSensor);
  int rightValue = analogRead(rightSensor);

  //判断是否检测到黑线
  if (leftValue < threshold && rightValue < threshold) {
    //两边都检测到黑线，第一次左转，第二次右转，第三次左转，第四次右转
    //请在此处添加代码
  } else if (leftValue < threshold) {
    //左边检测到黑线，左转
    digitalWrite(leftMotor, LOW);
    digitalWrite(rightMotor, HIGH);
  } else if (rightValue < threshold) {
    //右边检测到黑线，右转
    digitalWrite(leftMotor, HIGH);
    digitalWrite(rightMotor, LOW);
  } else {
    //两边都未检测到黑线，直行
    digitalWrite(leftMotor, HIGH);
    digitalWrite(rightMotor, HIGH);
  }
}
``