momentarySwitchAsToggle.ino

// constants for the pins
const int LEDPin = 2;
const int switchPin = 3;
// variables for the previous switch state and LED
int ledState = LOW;
int lastSwitchVal = LOW;

void setup() {
  // configure your pins
  pinMode(LEDPin, OUTPUT);
  pinMode(switchPin, INPUT);
}

void loop() {
  // read the value on the switchPin and store it
  // in a variable
  int switchVal = digitalRead(switchPin);

  // if the button state has changed:
  if (switchVal != lastSwitchVal && switchVal == HIGH) {
    ledState = !ledState;
  }
  
  // set the LED
  digitalWrite(LEDPin, ledState);

  // save the current reading. Next time through the loop
  // it'll be the lastSwitchVal
  lastSwitchVal = switchVal;

}