Object Avoiding Bot

byte la=2,lb=3,ra=5,rb=4,trig=6,echo=7,ls=8,rs=9;
float duration=1,distance;
float d;
void setup() {
  pinMode(la,OUTPUT);
  pinMode(lb,OUTPUT);
  pinMode(ra,OUTPUT);
  pinMode(rb,OUTPUT);
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(ls,INPUT);
  pinMode(rs,INPUT);
  Serial.begin(9600);
}
float dis(){
 digitalWrite(trig,LOW);
 delayMicroseconds(2);
 digitalWrite(trig,HIGH);
 delayMicroseconds(10); 
 digitalWrite(trig,LOW);
 duration=pulseIn(echo,HIGH);
 distance=duration*(0.034/2);
 Serial.print("distance =");
 Serial.println(distance);
 return distance;
 delay(1000);
}
void drive(){
  digitalWrite(ra,1);
  digitalWrite(la,1);
  digitalWrite(lb,0);
  digitalWrite(rb,0);
}
void stoper(){
  digitalWrite(ra,0);
  digitalWrite(la,0);
  digitalWrite(lb,0);
  digitalWrite(rb,0);
}
void reverse(){
  digitalWrite(ra,0);
  digitalWrite(la,0);
  digitalWrite(lb,1);
  digitalWrite(rb,1);
}
void right(){
  digitalWrite(ra,0);
  digitalWrite(la,1);
  digitalWrite(lb,0);
  digitalWrite(rb,1);
}
void left(){
  digitalWrite(ra,1);
  digitalWrite(la,0);
  digitalWrite(lb,1);
  digitalWrite(rb,0);
}
void loop() {
 d=dis();
 drive();
 if(d<=15)
 {
  if(digitalRead(ls)==1 && digitalRead(rs)==0)
  {
    stoper();
    delay(1000);
    reverse();
    delay(1000);
    right();
    delay(500);
    stoper();
  }
  else
  if(digitalRead(rs)==1 && digitalRead(ls)==0)
  {
    stoper();
    delay(1000);
    reverse();
    delay(1000);
    left();
    delay(500);
    stoper();
  }
  else
  {
    stoper();
    delay(1000);
    reverse();
    delay(1000);
    right();
    delay(2000);
  }
 }
 else
 if(digitalRead(ls)==1 || digitalRead(rs) ==1)
 {
  if(digitalRead(ls)==1)
  {
    stoper();
    delay(1000);
    reverse();
    delay(1000);
    right();
    delay(500);
  }
  else
  {
    stoper();
    delay(1000);
    reverse();
    delay(1000);
    left();
    delay(500);
  }
 }
}