Arduino Uno - HC-SR04 Distance Sensor Code Question

[christsall99]

Hello,

the block of code bellow is from an "Obstacle Avoidance Line Follower Robot" project, that I found on web. I created this project for personal use and I have the following problem. At first we define an integer value named distance which is the distance in cm that "sonar.ping_cm()" function returns. After that, it checks if distance is equal to 0 and its true then it sets the distance to 30. In the end it checks if distance is less or equal to 15 and if its true then it calls a function.
So what I really want is, when HC-SR04 sensor finds a distance that is lower or equal than 15 then the function moveForward should be called. I can't understand why lines 4, 5, 6 must be used in order to work. If I delete them, then my robot will keep calling the function moveForward() even if the distance is not less or equal to 15.

//CODE STARTS

1. void loop() {
2. delay(70);
3. int distance = sonar.ping_cm();
4. if (distance == 0) {
5. distance = 30;
6. }
7. if(distance<=15) {
8. moveForward();
9. }

//CODE ENDS

Thanks for your time, appreciate your help!

[anon73444976]

What's wrong with

if(distance<=15 && distance != 0) {
moveForward();
}

[J-M-L]

It depends on the library you use, but in most I have seen, The sonar returns zero when it cannot read the distance. it does not mean the distance is zero, just that it’s undefined (too far or too close)

[christsall99]

Good thought ! Thank you !