#define Echopin 9  
//ECHO PIN INPUT 9
#define Trigpin 10  
//TRIG PIN INPUT 10
#define Red_led 5 
//RED LED INPUT 5
#define Green_led 4  
//GREEN LED 4
float distance;  // for distance float 
int duration;
int ll = 500;    
//duration in 500

void setup() {
  pinMode (Trigpin, OUTPUT); 
  //OUTPUT from ULTRASONIC
  pinMode (Red_led, OUTPUT);   
  //PIN 5
  pinMode (Green_led, OUTPUT);  
  //PIN 4
  pinMode (Echopin, INPUT);  
  //INPUT from PIN
  Serial.begin(9600);  
}

void loop() //loop started 
 {
  digitalWrite(Trigpin, LOW);
  delayMicroseconds(500); // delay of 500 micros low
  digitalWrite(Trigpin, HIGH);
  delayMicroseconds(500); 
  //delay of 500 micros
  digitalWrite(Trigpin, LOW); //Trig is low 
  duration = pulseIn(Echopin, HIGH); // Duration for Echo
  //high echopin
  distance = duration * 0.034 / 2;  
  //duration in seconds
  delay (500);
  Serial.println (" ");
  Serial.print ("Distance = ");
  Serial.print (distance);
  Serial.print (" CM");
  Serial.println (" ");

  if (distance>100) 
  //if condition for green led
  {
    
    digitalWrite (Green_led, HIGH); 
    // GREEN LED is ON
    delay (500);  
    //delay of 500 
    digitalWrite (Red_led, LOW);
    delay (500); 
  }
  else 
  if (distance<100) 
  //if condition for red led
  {
    
    digitalWrite (Green_led, LOW);
    delay (500);
    digitalWrite (Red_led, HIGH); 
    // RED LED is ON
    delay (500); 
    //delay of 500
  }
}