char msg[80];  // array to store incoming characters
int idx = 0;   // index into array
int leDPins[] = {15, 2, 4, 5};
int numLeds = 4;
int i = 0;

int a ,b;

void setup() {
  // array of GPIO pins
  Serial.begin(115200);
  Serial.println("Program start ");

    for (i=0; i < numLeds; i++) {
    pinMode(ledPins[i], OUTPUT);
    }

  // Initialize each GPIO pin as an output and turn on the LED
  for (i = 3 i >= 0; i--) {
    digitalWrite(ledPins[i], LOW);
  
  }
//----------------------------------------------
a=0 , b =1;

if (  (a==1) && (b==1) ) // a==1 and b==1
    {
        for (i = 3; i >= 0; i--) 
        {
            digitalWrite(ledPins[i], HIGH);
        }
    }

if (  (a==0) && (b==0) ) // a==1 and b==1
    {
        for (i = 3; i >= 0; i--) 
        {
            digitalWrite(ledPins[i], LOW);
        }
    }


if (  (a==1) && (b==0) ) // a==1 and b==1
    {
       
            digitalWrite(ledPins[0], LOW);
            digitalWrite(ledPins[1], HIGH);
            digitalWrite(ledPins[2], LOW);
            digitalWrite(ledPins[3], HIGH);
    }    



if (  (a==0) && (b==1) ) // a==0 and b==1
    {
       
            digitalWrite(ledPins[0], HIGH);
            digitalWrite(ledPins[1], LOW);
            digitalWrite(ledPins[2], HIGH);
            digitalWrite(ledPins[3], LOW)
    }    

}


void loop() {
 

}