ultrasonic sensor with C

ultrasonic.c

#include<stdio.h>
#include<wiringPi.h>
 
#define TRIG 21 // trig GPIO 5
#define ECHO 22 // echo GPIO 6
 
int main(void){
    long startTime;
    long travelTime;
    int distance=0;
    
    if(wiringPiSetup()==-1) return 1;
        
    pinMode (TRIG, OUTPUT);
    pinMode (ECHO, INPUT);
    
    while(1){
        //초음파 발생코드
        digitalWrite (TRIG, LOW);
        delayMicroseconds(2);
        digitalWrite (TRIG, HIGH);
        delayMicroseconds(20);
        digitalWrite (TRIG, LOW);
        
        //거리측정코드
        while(digitalRead(ECHO) == LOW);
        startTime = micros();
        while(digitalRead(ECHO) == HIGH);
        travelTime = micros() - startTime;
        distance = travelTime / 58;
  
        if(distance < 400) printf( "Distance: %dcm\n", distance);
        delay(500);
    }

    return 0;
}