int sw = 3;
int led = 5;
boolean laststate;
boolean reading;
boolean state = LOW ;

void setup() {
 pinMode(led, OUTPUT);
 pinMode(sw, INPUT);  
}

void loop() {
  reading =digitalRead(sw);
     if(reading == LOW && laststate == HIGH){
      delay(10);
     if(digitalRead(sw)== LOW) state =!state;
     }
      digitalWrite(led,state);
      laststate = reading;
}