int t_p=5;
int e_p=18;
float ss=0.034;
long durn;
float dist_cm;

void setup() {

  Serial.begin(115200);
  pinMode(t_p,OUTPUT);
  pinMode(e_p,INPUT);

}

void loop() 
{
  digitalWrite(t_p,LOW);
  delayMicroseconds(2);
  digitalWrite(t_p,HIGH);
  delayMicroseconds(10);
  digitalWrite(t_p,LOW);
  durn=pulseIn(e_p,HIGH);
  dist_cm=durn*ss/2;
  Serial.print("distance= ");
  Serial.println(dist_cm);
  delay(100); 
}