LCD keypad shield buttons on an Arduino Uno

// The LCD keypad shield: a 16x2 LCD and five buttons on one analog pin.
//
//   LCD RS 8, E 9, D4..D7 on 4..7   (LiquidCrystal lcd(8, 9, 4, 5, 6, 7))
//   the buttons share A0 through a resistor ladder
//
// Each button shorts a different point of the ladder to ground, so A0 reads
// a different voltage for each: about 0 for RIGHT, 144 UP, 329 DOWN, 505
// LEFT, 741 SELECT and 1023 with none held. The sketch sorts a reading into
// the nearest one by the halfway points between them.

#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

const char *buttonAt(int reading) {
  if (reading < 72) return "RIGHT";
  if (reading < 237) return "UP";
  if (reading < 417) return "DOWN";
  if (reading < 623) return "LEFT";
  if (reading < 882) return "SELECT";
  return "none";
}

void setup() {
  lcd.begin(16, 2);
  lcd.print("Press a button");
}

void loop() {
  int reading = analogRead(A0);
  lcd.setCursor(0, 1);
  lcd.print(buttonAt(reading));
  lcd.print(" ");
  lcd.print(reading);
  lcd.print("      ");  // clear what a longer name left
  delay(100);
}