Arduino code — what's the use of while(0)?

Question

const int buttonPin = 2;    
int buttonState = 0;        

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

void loop() {
  buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH) {
    Serial.println("1");
    buttonState=LOW;
    delay(20000);
      while(0);
  }
}

Basically the code works like this:

the number of the pushbutton pin
variable for reading the pushbutton status
initialize the pushbutton pin as an input:
read the state of the pushbutton value:
check if the pushbutton is pressed. If it is, the buttonState is HIGH: send char 1 via Bluetooth:

I have an Arduino, HC 06 bluetooth module, a button and an app that makes a phonecall when the button is pressed (HC 06 send a byte, 1, to the app)

My question is, what's the while (0); for?

----ORIGINAL CODE---- const int PirSensor = 2; int motionState = 0;

void setup() {
  Serial.begin(9600);
  pinMode(PirSensor, INPUT);
}

void loop() {
  motionState = digitalRead(PirSensor);
  if (motionState == HIGH) {
    Serial.println("1"); 
    motionState = LOW;
    delay(20000);
//    while(0);
  }

}

It doesn't do anything, like that. Why did you put it there? — hobbs
Because I addapted my code from another that, instead of a button, it had an PIR motion detector. And i couldn´t understand what was the meaning of the while. — Josh Miles
@PedroFerreita Can you please show the original example then? — orhtej2
The most common context in which you see while (0); is at the end of a do { … } while (0); loop. I think it is fair to argue it is the only context in which while (0); is useful. As it stands, the empty body of the loop is never executed because the loop continuation condition is unconditionally false (zero). An alternative which is commonly seen is an infinite loop — while (1) { … } and sometimes that will have an empty loop body. This time the condition is unconditionally true (non-zero). — Jonathan Leffler
I have seen do{} while(0) used in pre-processor macros to guard against something but I can't remember what it was. I think it was to make sure that multi-statement macros that got put behind if statements without braces like they were single lines would act right. — Delta_G

matisa matisa · Accepted Answer · 2017-10-07T19:48:32

Well if I am not mistaken in this case nothing.

In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.

Note that if you do have a condition, a while loop must have an exit option, like this:

const int buttonPin = 2;    
int buttonState = 0;        

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

void loop() {
  buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH) {
    Serial.println("1");
    buttonState=LOW;
    delay(20000);
    int a =0;
      while(a==0){
        if (something)
          a=1;
      }
  }
}

Then on your chosen condition you will exit the loop.

Arduino code — what's the use of while(0)?

2 Answers