// initialise variables for rows/columns
  int col_1 = 4;
  int col_2 = 5;
  int col_3 = 6;

  int row_1 = 0;
  int row_2 = 1;
  int row_3 = 2;


void setup() {

  pinMode(0, OUTPUT);
  pinMode(1, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  for(int x = 1; x < 4; x++){
    for(int y = 1; y < 4; y++){

      turn_on_led(x, y);
      //delay(100);
    }

  }
   

  // turn_on_led(2, 3);
}

void turn_on_led(int x, int y){
  clear_leds();
  if (y == 1){
    digitalWrite(row_1, LOW);  
  }
  if (y == 2){
    digitalWrite(row_2, LOW);  
  }
  if (y == 3){
    digitalWrite(row_3, LOW);  
  }

  if (x == 1){
    digitalWrite(col_1, HIGH);  
  }
  if (x == 2){
    digitalWrite(col_2, HIGH);  
  }
  if (x == 3){
    digitalWrite(col_3, HIGH);  
  }
}

void clear_leds(){
  // turn off all leds
  digitalWrite(col_1, LOW);
  digitalWrite(col_2, LOW);
  digitalWrite(col_3, LOW);
  
  digitalWrite(row_1, HIGH);
  digitalWrite(row_2, HIGH);
  digitalWrite(row_3, HIGH);
}