http://www.forocoches.com/foro/showthread.php?t=5485473&page=10#post265346569

Arduino: Test Keypad Login (WITHOUT TESTING).ino

#include <Keypad.h>
#define COUNT(x) sizeof(x)/sizeof(*x)


HardwareSerial &pc = Serial;

class User
{
    public:
        String name;
        String pass;

        User( String name, String pass )
        {
            this->name = name;
            this->pass = pass;
        }
};
User users[] = {
    User("Paco",   "123A"),
    User("Carmen", "456B")
};

const byte pLED    = 13;
const byte pROWS[] = { 46, 48, 50, 52 };
const byte pCOLS[] = { 47, 49, 51, 53 };
const char KEYS[COUNT(pROWS)][COUNT(pCOLS)] = {
    {'1','2','3','A'},
    {'4','5','6','B'},
    {'7','8','9','C'},
    {'*','0','#','D'}
};
Keypad keypad   = Keypad( makeKeymap(KEYS), pROWS, pCOLS, COUNT(pROWS), COUNT(pCOLS) );
String password = "";


void setup()
{
    pinMode(pLED, OUTPUT);

    pc.begin(9600);
    while(!pc);
    pc.println(F("------------------ PROGRAMA INICIADO ------------------"));
    pc.println(F("-- INTRODUZCA SU CLAVE Y CONFIRME CON #, BORRE CON * --"));
    pc.println(F("-------------------------------------------------------"));
    pc.println();
}


void loop()
{
    char key = keypad.getKey();

    if( key > 0 )
    {
        if( key != '*' && key != '#' )
        {
            password += key;
        }
        else if( key == '*' )
        {
            pc.println(F("Clave cancelada"));
            password = "";
        }
        else if( key == '#' )
        {
            boolean found = false;
            byte    index;

            for( index=0 ; index < COUNT(users) && !found ; index++){
                found = users[index].pass.equalsIgnoreCase(password);
            }
            password = "";

            if( !found )
                pc.println(F("-> CREDENCIALES INCORRECTOS!\n"));
            else
            {
                pc.print(F("-> BIENVENIDO "));
                pc.print(users[index].name);
                pc.println("!\n");

                for( int i=0 ; i < 3 ; i++)
                {
                    digitalWrite(pLED, HIGH);
                    delay(500);
                    digitalWrite(pLED, LOW);
                    delay(200);
                }
            }
        }
    }

}