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

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);
}
}

Answer 1

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.

Answer 2

while(0) is most commonly used in macro definitions, specifically in those which are meant to be used like void functions or other instructions, like
#define inc(x) do { x = ((x)+1); } while (0)
The reason to use it is simply to make the use of the macro look like an invocation of a function by forcing the user to append a ; to the macro invocation. In the above example,
inc(a)
a = a*2;
would cause a compile error due to the missing ; after the while(0) the macro expands to, so you have to write
inc(a);
a = a*2;
which makes the code look more like inc was a function. Also, embedding the macro's code in a loop like this helps in preventing accidental use of the macro as an expression, akin to a void function. ( a = ((a)+1) is a valid expression, so b = inc(a) would be valid too (expands to b = a = ((a)+1)) if the macro did not contain the (semantically irrelevant) while loop.)