int random2;
int a;
int a1;
int a2;
#define ML_Ctrl 13  //define the direction control pin of left motor
#define ML_PWM 11   //define PWM control pin of left motor
#define MR_Ctrl 12  //define the direction control pin of right motor
#define MR_PWM 3    //define PWM control pin of right motor

#define Trig 5  //ultrasonic trig Pin
#define Echo 4  //ultrasonic echo Pin
int distance;
#define servoPin 9  //servo Pin
int pulsewidth;

int sensorPin = A3;   // select the input pin for the photocell
int sensorValue = 0;  // variable to store the value coming from the sensor

int INAPin = 13;
int INBPin = 12;

#define light_L_Pin A1  //define the pin of left photo resistor
#define light_R_Pin A2  //define the pin of right photo resistor
int left_light;
int right_light;

void Car_front() {
  digitalWrite(MR_Ctrl, LOW);
  analogWrite(MR_PWM, 200);
  digitalWrite(ML_Ctrl, LOW);
  analogWrite(ML_PWM, 200);
}
void Car_back() {
  digitalWrite(MR_Ctrl, HIGH);
  analogWrite(MR_PWM, 200);
  digitalWrite(ML_Ctrl, HIGH);
  analogWrite(ML_PWM, 200);
}
void Car_left() {
  digitalWrite(MR_Ctrl, LOW);
  analogWrite(MR_PWM, 255);
  digitalWrite(ML_Ctrl, HIGH);
  analogWrite(ML_PWM, 255);
}
void Car_right() {
  digitalWrite(MR_Ctrl, HIGH);
  analogWrite(MR_PWM, 255);
  digitalWrite(ML_Ctrl, LOW);
  analogWrite(ML_PWM, 255);
}
void Car_Stop() {
  digitalWrite(MR_Ctrl, LOW);
  analogWrite(MR_PWM, 0);
  digitalWrite(ML_Ctrl, LOW);
  analogWrite(ML_PWM, 0);
}

//The function to control servo
void procedure(int myangle) {
  for (int i = 0; i <= 50; i = i + (1)) {
    pulsewidth = myangle * 11 + 500;
    digitalWrite(servoPin, HIGH);
    delayMicroseconds(pulsewidth);
    digitalWrite(servoPin, LOW);
    delay((20 - pulsewidth / 1000));
  }
}
//The function to control ultrasonic sensor
float checkdistance() {
  digitalWrite(Trig, LOW);
  delayMicroseconds(2);
  digitalWrite(Trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(Trig, LOW);
  float distance = pulseIn(Echo, HIGH) / 58.00;  //58.20, that is, 2*29.1=58.2
  delay(10);
  return distance;
}
//****************************************************************
void setup() {
  pinMode(servoPin, OUTPUT);
  procedure(111);  //set servo to 90°

  pinMode(Trig, OUTPUT);
  pinMode(Echo, INPUT);
  pinMode(ML_Ctrl, OUTPUT);
  pinMode(ML_PWM, OUTPUT);
  pinMode(MR_Ctrl, OUTPUT);
  pinMode(MR_PWM, OUTPUT);

  pinMode(INAPin, OUTPUT);
  pinMode(INBPin, OUTPUT);
  pinMode(light_L_Pin, INPUT);
  pinMode(light_R_Pin, INPUT);
}

void loop() {
  random2 = random(1, 100);
  a = checkdistance();                  //assign the front distance detected by ultrasonic sensor to variable a
  sensorValue = analogRead(sensorPin);  // read the value from the sensor:
  left_light = analogRead(light_L_Pin);
  right_light = analogRead(light_R_Pin);

  if (sensorValue > 1000) {
    digitalWrite(INAPin, LOW);
    digitalWrite(INBPin, LOW);

    if (a < 20)  //when the front distance detected is less than 20
    {
      Car_Stop();                              //robot stops
      delay(500);                              //delay in 500ms
      procedure(160);                          //Ultrasonic platform turns left
      for (int j = 1; j <= 10; j = j + (1)) {  //for statement, the data will be more accurate if ultrasonic sensor detect a few times.
        a1 = checkdistance();                  //assign the left distance detected by ultrasonic sensor to variable a1
      }
      delay(300);
      procedure(20);  //Ultrasonic platform turns right
      for (int k = 1; k <= 10; k = k + (1)) {
        a2 = checkdistance();  //assign the right distance detected by ultrasonic sensor to variable a2
      }

      if (a1 < 50 || a2 < 50)  //robot will turn to the longer distance side when left or right distance is less than 50cm.
      {
        if (a1 > a2)  //left distance is greater than right side
        {
          procedure(111);  //Ultrasonic platform turns back to right ahead
          Car_left();      //robot turns left
          delay(500);      //turn left for 500ms
          Car_front();     //go front
        } else {
          procedure(111);
          Car_right();  //robot turns right
          delay(500);
          Car_front();  //go front
        }
      } else  //If both side is greater than or equal to 50cm, turn left or right randomly
      {
        if ((long)(random2) % (long)(2) == 0)  //When the random number is even
        {
          procedure(111);
          Car_left();  //tank robot turns left
          delay(500);
          Car_front();  //go front
        } else {
          procedure(111);
          Car_right();  //robot turns right
          delay(500);
          Car_front();  //go front
        }
      }
    } else  //If the front distance is greater than or equal to 20cm, robot car will go front
    {
      if (left_light > 650 && right_light > 650) {  //the value detected photo resistor，go front
        Car_front();
      } else if (left_light > 650 && right_light <= 650) {  //the value detected photo resistor，turn left
        Car_left();
      } else if (left_light <= 650 && right_light > 650) {  //the value detected photo resistor，turn right
        Car_right();
      }
    }
  } else {
    Car_Stop();
    delay(1000);
    analogWrite(INAPin, 255);
    digitalWrite(INBPin, LOW);
    delay(5000);
  }
}