const int LED1=4;
const int BUTTON=2;
boolean LastButton = LOW;
boolean CurrentButton = LOW;
boolean LedOn = false;

void setup()
 {
   pinMode(LED1, OUTPUT);
   pinMode(BUTTON, INPUT);
 }

boolean debounce(boolean Last)
{
  boolean Current = digitalRead(BUTTON);
  if(Last != Current)
  {
    delay(5);
    Current = digitalRead(BUTTON);
    return Current;
  }
 }

void loop()
{
  CurrentButton == debounce(LastButton);
 if (LastButton == LOW && CurrentButton == HIGH)
 {
   LedOn =! LedOn;
 }
 LastButton == CurrentButton;
 digitalWrite(LED1, LedOn);
}