int dirpin=4;
int stepin=5;

int back_step=6;

int start=2;
int stop=3;
const int front_rotation = 10000;

int duration;
int distance;
int duration_2;
int distance_2;

void setup() 
{
  pinMode(start, INPUT_PULLUP);    
  pinMode(stop, INPUT_PULLUP);
  Serial.begin(9600);
  pinMode(8, OUTPUT); 
  pinMode(9, INPUT); 
  pinMode(11, OUTPUT); 
  pinMode(10, INPUT); 
}

void loop() 
{

    //    FRONT-HC-SENSOR

  digitalWrite(8, LOW);
  delayMicroseconds(2);
  digitalWrite(8, HIGH);
  delayMicroseconds(10);
  digitalWrite(8, LOW);
  duration = pulseIn(9, HIGH);
  distance = duration * 0.034 / 2;

     //    BACK-HC-SENSOR

  digitalWrite(11, LOW);
  digitalWrite(11, HIGH);
  delayMicroseconds(10);
  digitalWrite(11, LOW);
  duration_2 = pulseIn(10, HIGH);
  distance_2 = duration_2 * 0.034 / 2;


  int s_val=digitalRead(start);
  int e_val=digitalRead(stop);

  if(s_val==0)  //IF START BUTTON PRESSED
  {
    if(distance>=15)
    {
      Serial.println("\nROBOT STARTED");
      digitalWrite(dirpin, HIGH);
      Serial.println("robot forward moving !");
      for(int x = 0 ; x <=front_rotation ; x++)
      {
        if(digitalRead(3)==0)
        {
          Serial.println("Stoped!");
          break;
        }

        if(x==1000)
        {
          back_gear();
          x=0;
        }
        digitalWrite(stepin, HIGH);
        delayMicroseconds(1000);
        digitalWrite(stepin, LOW);
        delayMicroseconds(3000);
      }
    }

    else if(distance<=15)
    {
      back_gear();
    }

  }

}

void back_gear()
{

  digitalWrite(7, LOW);
  digitalWrite(dirpin, LOW);
  Serial.println("Reversing.. !");
  for(int y = 0 ; y <=front_rotation ; y++)
    {
      digitalWrite(6, HIGH);
      delayMicroseconds(1000);
      digitalWrite(6, LOW);
      delayMicroseconds(3000);
      if(y==1000)
      {
        break;
      }
    }
}