How to exit while loop using keypad?

Question

I can't seem to be able to escape a while loop using a keypad button. I've tried the solution from this thread: https://forum.arduino.cc/index.php?topic=79932.0

Here's my code:

void alarm(){
  char customKey = customKeypad.getKey();

  while (customKey == NO_KEY){
    customKey = customKeypad.getKey();
    lcd.noDisplay();
    delay(750);// change for faster flash
    lcd.display();
    delay(750);// change for faster flash
  }
  lcd_home_screen();
}

I tried both == and != for the while (customKey == NO_KEY)

Additional info: I am calling this alarm function from another function inside my Loop. Here's the complete code:

void loop() {
  // keypad
  char customKey = customKeypad.getKey();    
  if (customKey == 'A'){
    main_program(5);
  }
}

int main_program(int duration){
  timer(duration);
  alarm();
}

Answer 1

Because you're using delay() within your while loop you have to ensure that you are pressing the key at the precise moment it is read.

You should not use delay().

Instead take a look at the BlinkWithoutDelay example in the IDE. And also consider implementing a Finite State Machine to know both if you're blinking and what state you're blinking currently is in.

Answer 2

To elaborate on Majenko's answer, you can create some enumeration types for the states, e.g.

enum EAlarmState 
{
   On,
   Off
};

EAlarmState _alarmState = EAlarmState::Off;

enum EBlinkState
{
    BlinkOn,
    BlinkOff,
};

EBlinkState _blinkState = EBlinkState::BlinkOff;

unsigned int long _lastBlinkTime = 0;

The _blinkState and _lastBlinkTime state will not be checked when _alarmState is off.

Now you can use something like this to check the states and the keypad (pseudo code):

void loop()
{
    checkKeypad();

    switch (_alarmState)
    {
    case EAlarmStateOn:
       if (millis() - _lastBlinkTime) >= 750)
       {
          `Blink off code`
          switch(_blinkState)
          {
          case EBlinkStateOn:
             _lastBlinkTime = millis();
             'Blink off code'
             _blinkState = EBlinkState::Off;
             break;

          `same for case EBlinkStateOff'
             break;

          default: // Error
             break;
          }
       }

And also create state checking and changing for the alarm itself.

It looks like a lot of code (and it will be), so split it in sub functions. But the most important is that the code is fairly easy to read (and thus maintain).