23. 4x4 Button to display the experimental routine (first)

#include <Keypad.h>
const byte ROWS = 4; // define four rows
const byte COLS = 4; // define four
char keys [ROWS] [COLS] = {
{'1 ', '2', '3 ',' A '},
{'4 ', '5', '6 ',' B '},
{'7 ', '8', '9 ',' C '},
{'*', '0 ',' # ',' D '}
};
// Connect 4 * 4 keypad row-bit port, the corresponding digital IO ports panel
byte rowPins [ROWS] = {2,3,4,5};
// Connect 4 * 4 buttons faithfully port, the corresponding digital IO ports panel
byte colPins [COLS] = {6,7,8,9};
// Call the function library function Keypad
Keypad keypad = Keypad (makeKeymap (keys), rowPins, colPins, ROWS, COLS);

void setup()
{
  Serial.begin (9600);
}

void loop()
{
  char key = keypad.getKey ();
  if (key != NO_KEY)
    Serial.println (key);
}