Bot in a Box object avoidance

#define PWMa 3
#define PWMb 5
#define AIN1 9
#define AIN2 8
#define BIN1 7
#define BIN2 6
#define Buzzer 2
#define pingPin 4
#define PhotoLeft 3
#define PhotoRight 2
#define Battery 1
#define LED 11
#define BumperLeft 10
#define BumperRight 12
long ping;
boolean right;
boolean left;
int left_state;
int right_state;

void setup()
{
  analogWrite(PWMa, 255);
  analogWrite(PWMb, 255);
  pinMode(AIN1, OUTPUT);
  pinMode(AIN2, OUTPUT);
  pinMode(BIN1, OUTPUT);
  pinMode(BIN2, OUTPUT);
  pinMode(LED, OUTPUT);
  pinMode(Buzzer, OUTPUT);
  pinMode(BumperLeft, INPUT);
  pinMode(BumperRight, INPUT);
  right = false;
  left = false;
  int left_state = LOW;
  int right_state = LOW;
}
void loop()
{
  left_state = digitalRead(BumperLeft);
  right_state = digitalRead(BumperRight);
  ping = Distance();
  digitalWrite(LED, HIGH);
  Forward();

  if (ping < 19)
  {
    digitalWrite(LED, LOW);
    digitalWrite(Buzzer, HIGH);
    Right();
    delay(500);
    digitalWrite(Buzzer, LOW);
  }

  if (left_state == HIGH)
  {
    digitalWrite(LED, LOW);
    digitalWrite(Buzzer, HIGH);
    Backward();
    delay(500);
    digitalWrite(Buzzer, LOW);
    Right();
    delay(500);
  }

   if (right_state == HIGH)
  {
    digitalWrite(LED, LOW);
    digitalWrite(Buzzer, HIGH);
    Backward();
    delay(500);
    digitalWrite(Buzzer, LOW);
    Left();
    delay(500);
  }
}

long Distance()
{
  long duration, cm;

  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);

  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);

  cm = microsecondsToCentimeters(duration);

  delay(100);
  return cm;
}

long microsecondsToCentimeters(long microseconds)
{
  return microseconds / 29 / 2;
}

void Forward()
{
  digitalWrite(AIN1, HIGH);
  digitalWrite(AIN2, LOW);
  digitalWrite(BIN1, HIGH);
  digitalWrite(BIN2, LOW);
}

void Backward()
{
  digitalWrite(AIN1, LOW);
  digitalWrite(AIN2, HIGH);
  digitalWrite(BIN1, LOW);
  digitalWrite(BIN2, HIGH);
}

void Right()
{
  digitalWrite(AIN1, HIGH);
  digitalWrite(AIN2, LOW);
  digitalWrite(BIN1, LOW);
  digitalWrite(BIN2, HIGH);
}

void Left()
{
  digitalWrite(AIN1, LOW);
  digitalWrite(AIN2, HIGH);
  digitalWrite(BIN1, HIGH);
  digitalWrite(BIN2, LOW);
}