Arduino - Liquid Crystal Display w/buttons

#include <LiquidCrystal.h>

/*******************************************************
This program allows the user to create a series of
messages on an LCD keypad screen that will display when
a particular key is pressed.

The only values that need to be changed are:
- upScreen, downScreen, leftScreen, rightScreen,
  selectScreen and noneScreen
- noneScreen is what will display when no buttons are
  being pressed.

Messages must be exactly 16 characters long and contain
2 lines. You must use spaces to clear old messages!

Modified from code at: https://www.dfrobot.com/wiki/index.php/Arduino_LCD_KeyPad_Shield_(SKU:_DFR0009)
********************************************************/

// select the pins used on the LCD panel
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

// define some values used by the panel and buttons
int lcd_key     = 0;
int adc_key_in  = 0;
#define btnRIGHT  0
#define btnUP     1
#define btnDOWN   2
#define btnLEFT   3
#define btnSELECT 4
#define btnNONE   5

// this is where you put your messages, using this format:
//                        "FIRST LINE------", "SECOND LINE-----"
//                         1234567890123456    1234567890123456
char* upScreen[]      = { "You are pressing", "the  UP   button" }; // displays when UP is pressed
char* downScreen[]    = { "You are pressing", "the DOWN button " }; // displays when DOWN is pressed
char* leftScreen[]    = { "You are pressing", "the LEFT button " }; // displays when LEFT is pressed
char* rightScreen[]   = { "You are pressing", "the RIGHT button" }; // displays when RIGHT is pressed
char* selectScreen[]  = { "You are pressing", "  SELECT  button" }; // displays when SELECT is pressed
char* noneScreen[]    = { "Try pressing one", "of the buttons! " }; // displays when SELECT is pressed

// read the buttons
int read_LCD_buttons()
{
  adc_key_in = analogRead(0);      // read the value from the sensor
  if (adc_key_in > 1000) return btnNONE; // We make this the 1st option for speed reasons since it will be the most likely result
  int rightButtonValue = 0;
  int upButtonValue = 143;
  int downButtonValue = 328;
  int leftButtonValue = 504;
  int selectButtonValue = 740;

  // if (adc_key_in == rightButtonValue)   return btnRIGHT;
  if (adc_key_in >= (rightButtonValue - 10) && adc_key_in <= (rightButtonValue + 10))  return btnRIGHT;
  if (adc_key_in >= (upButtonValue - 10) && adc_key_in <= (upButtonValue + 10))  return btnUP;
  if (adc_key_in >= (downButtonValue - 10) && adc_key_in <= (downButtonValue + 10))  return btnDOWN;
  if (adc_key_in >= (leftButtonValue - 10) && adc_key_in <= (leftButtonValue + 10))  return btnLEFT;
  if (adc_key_in >= (selectButtonValue - 10) && adc_key_in <= (selectButtonValue + 10))  return btnSELECT;

  return btnNONE;  // when all others fail, return this...
}

void setup()
{
  lcd.begin(16, 2);              // start the library
  lcd.setCursor(0,0);
  lcd.print(noneScreen[0]);
  lcd.setCursor(0,1);
  lcd.print(noneScreen[1]);
}


void loop()
{

  lcd_key = read_LCD_buttons();  // read the buttons

  switch (lcd_key)               // depending on which button was pushed, we perform an action
   {

   case btnRIGHT:
     {
       lcd.setCursor(0,0);
       lcd.print(rightScreen[0]);
       lcd.setCursor(0,1);
       lcd.print(rightScreen[1]);
     break;
     }

   case btnLEFT:
     {
       lcd.setCursor(0,0);
       lcd.print(leftScreen[0]);
       lcd.setCursor(0,1);
       lcd.print(leftScreen[1]);
     break;
     }

   case btnUP:
     {
     // reset the display
     lcd.setCursor(0,0);
     lcd.print(upScreen[0]);
     lcd.setCursor(0,1);
     lcd.print(upScreen[1]);
     break;
     }

   case btnDOWN:
     {
     // reset the display
     lcd.setCursor(0,0);
     lcd.print(downScreen[0]);
     lcd.setCursor(0,1);
     lcd.print(downScreen[1]);
     break;
     }

   case btnSELECT:
     {
     lcd.setCursor(0,0);
     lcd.print(selectScreen[0]);
     lcd.setCursor(0,1);
     lcd.print(selectScreen[1]);
     break;
     }

   case btnNONE:
     {
      lcd.setCursor(0,0);
      lcd.print(noneScreen[0]);
      lcd.setCursor(0,1);
      lcd.print(noneScreen[1]);
     break;
     }

   } // end switch

} // end void loop