Change LEDs Between Green and Red

/*

Keypad Shield Example

This example shows an application on 1Sheeld's keypad shield.

By using this example,  when you prees on a key green led turn on and 
when you press to another key red led turn on
when you prees on a key white led turn on and 
when you press to another key yellow led turn on

OPTIONAL:
To reduce the library compiled size and limit its memory usage, you
can specify which shields you want to include in your sketch by
defining CUSTOM_SETTINGS and the shields respective INCLUDE_ define. 

*/

#define CUSTOM_SETTINGS
#define INCLUDE_KEYPAD_SHIELD

/* Include 1Sheeld library. */
#include <OneSheeld.h>
int A, B, C, D; //vaiables with names of buttons in keypad
/* A name for the LED on pin 8. */
int yellow = 8;
/* A name for the LED on pin 9. */
int green = 9;
/* A name for the LED on pin 10. */
int white = 10;
/* A name for the LED on pin 11. */
int red = 11;

void setup() 
{
  /* Start communication. */
  OneSheeld.begin();
  /* Set LEDs A, B, C and D as output. */
  pinMode(yellow,OUTPUT);
  pinMode(red,OUTPUT);
  pinMode(green,OUTPUT);
  pinMode(white,OUTPUT);
}

void loop()
{
  /* If keypad's button A is pressed. */
  if(Keypad.isRowPressed(0) && Keypad.isColumnPressed(3))
  {
    A = 1; // press A 
    B = 0;
    C = 0;
    D = 0;
  }
  
  else if(Keypad.isRowPressed(1) && Keypad.isColumnPressed(3))
  {
    A = 0;
    B = 1;// press B
    C = 0;
    D = 0;
  }
  
   else if(Keypad.isRowPressed(2) && Keypad.isColumnPressed(3))
  {
    A = 0;
    B = 0;
    C = 1;  // press c
    D = 0;
  }

   else if(Keypad.isRowPressed(3) && Keypad.isColumnPressed(3))
  {
    A = 0;
    B = 0;
    C = 0;
    D = 1; // press D
  }
  else
  {
    /* Turn off all of LEDs. */
    digitalWrite(yellow,LOW);
    digitalWrite(green,LOW);
    digitalWrite(white,LOW);
    digitalWrite(red,LOW);
  }
  if(A) //press button A
    digitalWrite(yellow, HIGH);
  if(B) //press button B
    digitalWrite(green, HIGH);
  if(C) //press button C
    digitalWrite(white, HIGH);
  if(D) //press button D
    digitalWrite(red, HIGH);
}