Obstacle Avoiding Robot

int trigPin = 9;      // Trig Pin Of HC-SR04
int echoPin = 8;     // Echo Pin Of HC-SR04
int revleft4 = 10; // Motor Pins
int fwdleft5 = 11;
int revright6 = 12;
int fwdright7 = 13;
long duration, distance;

void setup() {
  Serial.begin(9600);
  pinMode(revleft4, OUTPUT); // Set Motor Pins As O/P
  pinMode(fwdleft5, OUTPUT);
  pinMode(revright6, OUTPUT);
  pinMode(fwdright7, OUTPUT);
  pinMode(trigPin, OUTPUT); // Set Trig Pin As O/P To Transmit Waves
  pinMode(echoPin, INPUT); //Set Echo Pin As I/P To Recieve Reflected Waves
}

void loop() {

  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);   
  digitalWrite(trigPin, HIGH); // Transmit Waves For 10us
  delayMicroseconds(10);
  duration = pulseIn(echoPin, HIGH); // Recieve Reflected Waves
  distance = duration / 58.2; // Get Distance
  delay(10);
  if (distance > 20) // Condition For Absence Of Obstacle            
  {
    digitalWrite(fwdright7, HIGH); // Move Forward
    digitalWrite(revright6, LOW);
    digitalWrite(fwdleft5, HIGH);                                
    digitalWrite(revleft4, LOW);                                                       
  }

  if (distance < 20) // Condition For Presence Of Obstacle
  {
    digitalWrite(fwdright7, LOW); //Stop                
    digitalWrite(revright6, LOW);
    digitalWrite(fwdleft5, LOW);                                
    digitalWrite(revleft4, LOW);
    delay(500);
    digitalWrite(fwdright7, LOW); // Move Backward             
    digitalWrite(revright6, HIGH);
    digitalWrite(fwdleft5, LOW);                                
    digitalWrite(revleft4, HIGH);
    delay(500);
    digitalWrite(fwdright7, LOW);  //Stop                
    digitalWrite(revright6, LOW);
    digitalWrite(fwdleft5, LOW);                                
    digitalWrite(revleft4, LOW);  
    delay(100);  
    digitalWrite(fwdright7, HIGH); // Move Left       
    digitalWrite(revright6, LOW);   
    digitalWrite(revleft4, LOW);                                 
    digitalWrite(fwdleft5, LOW);  
    delay(500);
  }

}