int btnpin = 3;
int ledpin = 10; //sets the constant ledpin to 13
boolean lastButton = LOW; //bool can be high or low, and here I set it to start low.
boolean currentButton = LOW; //keeps track of current button state
boolean ledon = false; //VARIABLE TO let us track current state of the led. starts with 'false'



void setup() {
  pinMode(btnpin, INPUT_PULLUP); //'pulls' the power of the button up to 5 v ('high') reading when it is not pressed.
  pinMode(ledpin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  currentButton = debounce(lastButton);
  int sensor = digitalRead(btnpin);
  if (lastButton == HIGH && currentButton == LOW) {
    ledon = !ledon;
  }
  lastButton = currentButton;
  digitalWrite(ledpin, ledon);
}

boolean debounce (boolean last) { //debounce function
  boolean current = digitalRead(btnpin);
  if (last != current)
  {
    delay (5);
    current = digitalRead(btnpin);
  }
  return (current);
}