#define Echopin 12  
//ECHO PIN INPUT 12
#define Trigpin 6   
// TRIG PIN INPUT 6
#define Red_led 7  
// RED LED INPUT 7
#define Green_led 8   
//GREEN LED 8
float distance;  // for distance float 
int duration;
int ll = 1000;    
// duration in 1000

void setup() {
  pinMode (Trigpin, OUTPUT); 
  // OUTPUT from ULTRASONIC
  pinMode (Red_led, OUTPUT);   
  // PIN 7
  pinMode (Green_led, OUTPUT);  
  // PIN 8
  pinMode (Echopin, INPUT);  
  // INPUT from PIN
  Serial.begin(9600);  
  // begin the serial monitor
  digitalWrite (Red_led, LOW);  // initially RED LED is OFF
  digitalWrite (Green_led, LOW); 
  // initial GREEN LED is OFF
}

void loop() //loop started 
 {
  digitalWrite(Trigpin, LOW);
  delayMicroseconds(1000); // delay of 1000 micros low
  digitalWrite(Trigpin, HIGH);
  delayMicroseconds(1000); 
  //delay of 1000 micros
  digitalWrite(Trigpin, LOW);
  duration = pulseIn(Echopin, HIGH); //high echopin
  distance = duration * 0.034 / 2;  
  //duration in seconds
  delay (1000);
  Serial.println (" ");
  Serial.print ("Distance = ");
  Serial.print (distance);
  Serial.print (" CM");
  Serial.println (" ");

  if (distance>100) 
  //if condition for green led
  {
    Serial.println ("No one is there in 100 cm"); // out of range
    digitalWrite (Green_led, HIGH); 
    // GREEN LED is ON
    delay (1000);  
    //delay of 1000 
    digitalWrite (Red_led, LOW);
    delay (1000);
    digitalWrite (Green_led, HIGH);
  }
  else 
  if (distance<100) //if condition for red led
  {
    Serial.println ("Some is there in 100 cm");  //in the range
    digitalWrite (Green_led, LOW);
    delay (1000);
    digitalWrite (Red_led, HIGH); // RED LED is ON
    delay (1000); 
    //delay of 2000
    digitalWrite (Red_led, HIGH);
    delay (1000);
  }
}