//motor shield pin
int dirR = 12;
int speedR = 10;
int dirL = 13;
int speedL = 11;

//ultrasonic pin
int _ = _;
int _ = _;
long _;
int _;

void setup()
{
  pinMode(dirR, OUTPUT);
  pinMode(speedR, OUTPUT);
  pinMode(dirL, OUTPUT);
  pinMode(speedL, OUTPUT);
  pinMode(_, INPUT); //echo
  pinMode(_, OUTPUT); //trig
  Serial.begin(9600);
}

void forward(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, HIGH);
  analogWrite(speedR, a);
  digitalWrite(dirL, HIGH);
  analogWrite(speedL, b);
}

void backward(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, LOW);
  analogWrite(speedR, a);
  digitalWrite(dirL, LOW);
  analogWrite(speedL, b);
}

void right(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, LOW);
  analogWrite(speedR, a);
  digitalWrite(dirL, HIGH);
  analogWrite(speedL, b);
}

void left(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, HIGH);
  analogWrite(speedR, a);
  digitalWrite(dirL, LOW);
  analogWrite(speedL, b);
}

void stop()
{
  analogWrite(speedR, 0);
  analogWrite(speedL, 0);
}

void _() //ultrasonic
{
  digitalWrite(_, LOW); //ultrasonic trig pin
  delayMicroseconds(2);

  //ultrasonic trig pin
  digitalWrite(_, HIGH);
  delayMicroseconds(10);
  digitalWrite(_, LOW);

  //ultrasonic echo pin
  _ = pulseIn(_, HIGH);
  _ = _ * 0.034 / 2;
}

void loop()
{
  _(); //ultrasonic
  Serial.print("Distance: ");
  Serial.println(_);

  if ( _ > _ && _ < _ )
  {
    stop();
    delay(_);
    _(_, _); //reverse
    delay(_);
    _(_, _); //turn
    delay(_);
  }
  else
  {
    _(_, _); //forward
  }
}