Why does my if function keep looping?

sorry if has been addressed before, can't find other thread.  i'm building cosplay prop (lightning gun) , having issues if function in code.  when pull trigger (momentary switch), cues lightning light.  it's supposed turn off, fade on , stay on.  when pull trigger, fades on, loops if statement forever.

in looking @ serial monitor, keeps spitting out alternate 1s , 0s works through if statement on , over.  it's program thinks trigger held down (or pulled repeatedly), it's not.  digitalread(trigger) should notice value no longer 0 , not perform if function, right?  appreciated.

code: [select]

int lightning = 10;
int trigger = 2;
//int triggerval = 1;

void setup() {
  serial.begin(9600);
  pinmode(trigger, input_pullup);
  pinmode(lightning, output);
}

void loop() {
  int triggerval = digitalread(trigger);
  if(triggerval == 0) {
    serial.println(triggerval);     // shows me 0 in serial monitor trigger pulled
    analogwrite(lightning,0);
    for(int fadevalue1 = 0 ; fadevalue1 <= 255; fadevalue1 +=20) {
      analogwrite(lightning,fadevalue1);
      delay(50);
    }
    triggerval = 1;     // trying reset trigger value "off"
    serial.println(triggerval);     // part shows me 1 in serial monitor
  }
}

then triggerpin must reading low.  perhaps due noise.  try decent external pullup resistor such as
2.2k, internal pullup may weak.

Arduino Forum > Using Arduino > Programming Questions > Why does my if function keep looping?

arduino