const int led_1=10;
const int led_2=11;
const int led_3=12;
const int led_4=13;

const int incr_btn=7;
const int decr_btn=8;

int led_counter=0;


void setup()
{
  pinMode(led_1,OUTPUT);
    pinMode(led_2,OUTPUT);
      pinMode(led_3,OUTPUT);
        pinMode(led_4,OUTPUT);
          
            pinMode(incr_btn,INPUT);
              pinMode(decr_btn,INPUT);
                
                  //Serial.begin(9600);
                  }

                  void loop()
                  {
                    if(digitalRead(incr_btn)) // increment counter when PIN 7 is HIGH
                      {
                          led_counter++; 
                              //Serial.println(led_counter);
                                }
                                  if(digitalRead(decr_btn)) // decrement counter when PIN 8 is HIGH
                                    {
                                        led_counter--;
                                            //Serial.println(led_counter);
                                              }
                                                
                                                  switch(led_counter)
                                                    {
                                                        
                                                            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,HIGH);
                                                                                                                            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,HIGH);
                                                                                                                                                                digitalWrite(led_4,LOW);
                                                                                                                                                                    break;
                                                                                                                                                                        
                                                                                                                                                                            case 4:
                                                                                                                                                                                digitalWrite(led_1,HIGH);
                                                                                                                                                                                    digitalWrite(led_2,HIGH);
                                                                                                                                                                                        digitalWrite(led_3,HIGH);
                                                                                                                                                                                            digitalWrite(led_4,HIGH);
                                                                                                                                                                                                break;
                                                                                                                                                                                                    
                                                                                                                                                                                                        default:
                                                                                                                                                                                                            digitalWrite(led_1,LOW);
                                                                                                                                                                                                                digitalWrite(led_2,0);
                                                                                                                                                                                                                    digitalWrite(led_3,0);
                                                                                                                                                                                                                        digitalWrite(led_4,LOW);
                                                                                                                                                                                                                        led_counter=0;
                                                                                                                                                                                                                            break;
                                                                                                                                                                                                                              }
                                                                                                                                                                                                                                
                                                                                                                                                                                                                                  
                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                      delay(100);
                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                        }