const int buttonPin = A0;     // the number of the pushbutton pin
const int ledPin =  A1;      // the number of the LED pin

byte oldPinState = HIGH;

void setup ()
  {
  pinMode (buttonPin, INPUT_PULLUP);  
  pinMode (ledPin, OUTPUT);
  }  // end of setup

void loop ()
  {
  byte pinState = digitalRead (buttonPin);
  if (pinState != oldPinState)
    {
    delay (10);  // debounce 
    if (pinState == LOW)
      digitalWrite (ledPin, !digitalRead (ledPin));  // toggle pin
    oldPinState = pinState;  // remember new state
    }  // end of if pin state change
  }  // end of loop