Make a binary 4 bit counter using Arduino

Instruction:

1. L.E.Ds act as binary 1 and 0 (LED ON=1; LED OFF= 0). 
2. Write a code that will continuously count from 0 to max. Each number will be displayed for 2 seconds.

Design:

 Code:

/*
Name: 4 bit counter.
*/

int led_1 = 1; //0th bit led pin
int led_2 = 2; //1st bit led pin
int led_3 = 3; //2nd bit led pin
int led_4 = 4; //3rd bit led pin

void setup() {
  //setup the pinmode as output
  pinMode(led_1, OUTPUT); 
  pinMode(led_2, OUTPUT);
  pinMode(led_3, OUTPUT);
  pinMode(led_4, OUTPUT);
}

void loop() {
  //loop from 0 to max
  for(int i=0; i<=15; i++) {
    //switch-case for 0-max
    switch(i) {
     case 0:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, LOW); 
      break;
     case 1:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, LOW); 
      break;
     case 2:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, LOW); 
      break;
     case 3:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, LOW); 
      break;
     case 4:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, LOW); 
        break;
     case 5:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, LOW); 
        break;
     case 6:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, LOW); 
      break;
     case 7:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, LOW); 
        break;
     case 8:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, HIGH); 
        break;
     case 9:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, HIGH); 
        break;
     case 10:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, HIGH); 
        break;
     case 11:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, HIGH); 
        break;
     case 12:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, HIGH); 
        break;
     case 13:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, HIGH); 
        break;
     case 14:
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, HIGH); 
        break;
     case 15:
        digitalWrite(led_1, HIGH); 
        digitalWrite(led_2, HIGH); 
        digitalWrite(led_3, HIGH); 
        digitalWrite(led_4, HIGH); 
        break;
     default:
        //reset at default
        digitalWrite(led_1, LOW); 
        digitalWrite(led_2, LOW); 
        digitalWrite(led_3, LOW); 
        digitalWrite(led_4, LOW);
        break;
    }
    delay(2000); //Each number will be displayed for 2 seconds.
  }
}