Blink 3

const int LED = 13; //LED is in port 13
const int BUTTON = 7; //BUTTON is in port 7

int val = 0; //state of the button
int old_val = 0; //previous state of button

int state = 0; // 0 = LED off // 1 = LED on

void setup(){
  pinMode(LED, OUTPUT); //port 13 is set to output;
  pinMode(BUTTON, INPUT); //port 7 is set to input

}

void loop(){
  val = digitalRead(BUTTON); // value of val is the state of button

  //check if a transition has happened
  //if there was, 
  if ((val == HIGH) && (old_val == LOW)){
    state = 1 - state;
  }

  old_val = val; //set most recent val to old_val

  if (state ==1){
    digitalWrite(LED, HIGH); //turn port 13 to high
  }else{
    digitalWrite(LED, LOW); //if state is not 1, port 13 to low
  }
}