用C语言写一个循迹小车的代码，使其在遇到圆圈路线时，只转一圈，就退出圆圈

循迹小车的代码需要结合具体的硬件来编写，这里给出一个基于Arduino开发板的循迹小车代码示例，可以在遇到圆圈路线时只转一圈，然后退出圆圈。

#define L1 2
#define L2 3
#define R1 4
#define R2 5
#define Sensor1 A0
#define Sensor2 A1
#define Sensor3 A2
#define Sensor4 A3
#define Sensor5 A4
#define Sensor6 A5

void setup() {
  pinMode(L1, OUTPUT);
  pinMode(L2, OUTPUT);
  pinMode(R1, OUTPUT);
  pinMode(R2, OUTPUT);
  pinMode(Sensor1, INPUT);
  pinMode(Sensor2, INPUT);
  pinMode(Sensor3, INPUT);
  pinMode(Sensor4, INPUT);
  pinMode(Sensor5, INPUT);
  pinMode(Sensor6, INPUT);
}

void loop() {
  int s1 = digitalRead(Sensor1);
  int s2 = digitalRead(Sensor2);
  int s3 = digitalRead(Sensor3);
  int s4 = digitalRead(Sensor4);
  int s5 = digitalRead(Sensor5);
  int s6 = digitalRead(Sensor6);

  if (s1 == HIGH && s2 == HIGH && s3 == HIGH && s4 == LOW && s5 == LOW && s6 == LOW) {
    int count = 0;
    while (count < 100) {
      digitalWrite(L1, HIGH);
      digitalWrite(L2, LOW);
      digitalWrite(R1, HIGH);
      digitalWrite(R2, LOW);
      delay(10);
      count++;
    }
  }
  else {
    if (s4 == HIGH && s5 == HIGH) {
      digitalWrite(L1, HIGH);
      digitalWrite(L2, LOW);
      digitalWrite(R1, HIGH);
      digitalWrite(R2, LOW);
    }
    else if (s1 == HIGH && s2 == LOW && s3 == LOW) {
      digitalWrite(L1, LOW);
      digitalWrite(L2, HIGH);
      digitalWrite(R1, HIGH);
      digitalWrite(R2, LOW);
    }
    else if (s1 == LOW && s2 == LOW && s3 == HIGH) {
      digitalWrite(L1, HIGH);
      digitalWrite(L2, LOW);
      digitalWrite(R1, LOW);
      digitalWrite(R2, HIGH);
    }
    else if (s1 == LOW && s2 == HIGH && s3 == HIGH) {
      digitalWrite(L1, LOW);
      digitalWrite(L2, HIGH);
      digitalWrite(R1, LOW);
      digitalWrite(R2, HIGH);
    }
    else if (s1 == HIGH && s2 == HIGH && s3 == HIGH && s4 == HIGH && s5 == HIGH && s6 == HIGH) {
      digitalWrite(L1, LOW);
      digitalWrite(L2, LOW);
      digitalWrite(R1, LOW);
      digitalWrite(R2, LOW);
    }
    else {
      digitalWrite(L1, LOW);
      digitalWrite(L2, HIGH);
      digitalWrite(R1, HIGH);
      digitalWrite(R2, LOW);
    }
  }
}

在这个代码中，我们通过读取循迹小车上的六个红外传感器的状态来判断小车的运动方向。当小车遇到圆圈路线时，我们通过设置一个计数器来控制小车只转一圈，然后退出圆圈。