how to stop a loop arduino

Question

I have this loop, how would I end the loop?

 void loop() {
      // read the pushbutton input pin:

       a ++;
      Serial.println(a);
        analogWrite(speakerOut, NULL);

      if(a > 50 && a < 300){
      analogWrite(speakerOut, 200);
      }

      if(a <= 49){
        analogWrite(speakerOut, NULL);
      }

      if(a >= 300 && a <= 2499){
          analogWrite(speakerOut, NULL);
      }

Answer 1

This isn't published on Arduino.cc but you can in fact exit from the loop routine with a simple exit(0);

This will compile on pretty much any board you have in your board list. I'm using IDE 1.0.6. I've tested it with Uno, Mega, Micro Pro and even the Adafruit Trinket

void loop() {
// All of your code here

/* Note you should clean up any of your I/O here as on exit, 
all 'ON'outputs remain HIGH */

// Exit the loop 
exit(0);  //The 0 is required to prevent compile error.
}

I use this in projects where I wire in a button to the reset pin. Basically your loop runs until exit(0); and then just persists in the last state. I've made some robots for my kids, and each time the press a button (reset) the code starts from the start of the loop() function.

Answer 2

Arduino specifically provides absolutely no way to exit their loop function, as exhibited by the code that actually runs it:

setup();

for (;;) {
    loop();
    if (serialEventRun) serialEventRun();
}

Besides, on a microcontroller there isn't anything to exit to in the first place.

The closest you can do is to just halt the processor. That will stop processing until it's reset.