If you have a lot of button inputs for a project, keeping track of them (whether they’re pressed, just pressed or just released) and debouncing can get a bit hairy. here is some sample code that will keep track of as many buttons as you’d like. The example shows 6. To change the pins or number of buttons, just put them in the array called “buttons” and the rest of the code will automatically adjust. (The code is in Arduino-ese but its pretty much just straight up C)
Enjoy!

#define DEBOUNCE 10  // button debouncer, how many ms to debounce, 5+ ms is usually plenty

// here is where we define the buttons that we'll use. button "1" is the first, button "6" is the 6th, etc
byte buttons[] = {14, 15, 16, 17, 18, 19}; // the analog 0-5 pins are also known as 14-19
// This handy macro lets us determine how big the array up above is, by checking the size
#define NUMBUTTONS sizeof(buttons)
// we will track if a button is just pressed, just released, or 'currently pressed' 
byte pressed[NUMBUTTONS], justpressed[NUMBUTTONS], justreleased[NUMBUTTONS];

void setup() {
  byte i;

  // set up serial port
  Serial.begin(9600);
  Serial.print("Button checker with ");
  Serial.print(NUMBUTTONS, DEC);
  Serial.println(" buttons");

  // pin13 LED
  pinMode(13, OUTPUT);

  // Make input & enable pull-up resistors on switch pins
  for (i=0; i< NUMBUTTONS; i++) {
    pinMode(buttons[i], INPUT);
    digitalWrite(buttons[i], HIGH);
  }
}

void check_switches()
{
  static byte previousstate[NUMBUTTONS];
  static byte currentstate[NUMBUTTONS];
  static long lasttime;
  byte index;

  if (millis() < lasttime) {
     // we wrapped around, lets just try again
     lasttime = millis();
  }

  if ((lasttime + DEBOUNCE) > millis()) {
    // not enough time has passed to debounce
    return;
  }
  // ok we have waited DEBOUNCE milliseconds, lets reset the timer
  lasttime = millis();

  for (index = 0; index < NUMBUTTONS; index++) {
    justpressed[index] = 0;       // when we start, we clear out the "just" indicators
    justreleased[index] = 0;

    currentstate[index] = digitalRead(buttons[index]);   // read the button

    /*     
    Serial.print(index, DEC);
    Serial.print(": cstate=");
    Serial.print(currentstate[index], DEC);
    Serial.print(", pstate=");
    Serial.print(previousstate[index], DEC);
    Serial.print(", press=");
    */

    if (currentstate[index] == previousstate[index]) {
      if ((pressed[index] == LOW) && (currentstate[index] == LOW)) {
          // just pressed
          justpressed[index] = 1;
      }
      else if ((pressed[index] == HIGH) && (currentstate[index] == HIGH)) {
          // just released
          justreleased[index] = 1;
      }
      pressed[index] = !currentstate[index];  // remember, digital HIGH means NOT pressed
    }
    //Serial.println(pressed[index], DEC);
    previousstate[index] = currentstate[index];   // keep a running tally of the buttons
  }
}

void loop() {
  check_switches();      // when we check the switches we'll get the current state

  for (byte i = 0; i < NUMBUTTONS; i++) {
    if (justpressed[i]) {
      Serial.print(i, DEC);
      Serial.println(" Just pressed");
      // remember, check_switches() will CLEAR the 'just pressed' flag
    }
    if (justreleased[i]) {
      Serial.print(i, DEC);
      Serial.println(" Just released");
      // remember, check_switches() will CLEAR the 'just pressed' flag
    }
    if (pressed[i]) {
      Serial.print(i, DEC);
      Serial.println(" pressed");
      // is the button pressed down at this moment
    }
  }
}

if you want, you can even run the button checker in the background, which can make for a very easy interface. Remember that you’ll need to clear “just pressed”, etc. after checking or it will be “stuck” on

#define DEBOUNCE 10  // button debouncer, how many ms to debounce, 5+ ms is usually plenty

// here is where we define the buttons that we'll use. button "1" is the first, button "6" is the 6th, etc
byte buttons[] = {14, 15, 16, 17, 18, 19}; // the analog 0-5 pins are also known as 14-19
// This handy macro lets us determine how big the array up above is, by checking the size
#define NUMBUTTONS sizeof(buttons)
// we will track if a button is just pressed, just released, or 'currently pressed' 
volatile byte pressed[NUMBUTTONS], justpressed[NUMBUTTONS], justreleased[NUMBUTTONS];

void setup() {
  byte i;

  // set up serial port
  Serial.begin(9600);
  Serial.print("Button checker with ");
  Serial.print(NUMBUTTONS, DEC);
  Serial.println(" buttons");

  // pin13 LED
  pinMode(13, OUTPUT);

  // Make input & enable pull-up resistors on switch pins
  for (i=0; i< NUMBUTTONS; i++) {
    pinMode(buttons[i], INPUT);
    digitalWrite(buttons[i], HIGH);
  }

  // Run timer2 interrupt every 15 ms 
  TCCR2A = 0;
  TCCR2B = 1<<CS22 | 1<<CS21 | 1<<CS20;

  //Timer2 Overflow Interrupt Enable
  TIMSK2 |= 1<<TOIE2;

}

SIGNAL(TIMER2_OVF_vect) {
  check_switches();
}

void check_switches()
{
  static byte previousstate[NUMBUTTONS];
  static byte currentstate[NUMBUTTONS];
  static long lasttime;
  byte index;

  if (millis() < lasttime) {
     // we wrapped around, lets just try again
     lasttime = millis();
  }

  if ((lasttime + DEBOUNCE) > millis()) {
    // not enough time has passed to debounce
    return;
  }
  // ok we have waited DEBOUNCE milliseconds, lets reset the timer
  lasttime = millis();

  for (index = 0; index < NUMBUTTONS; index++) {

    currentstate[index] = digitalRead(buttons[index]);   // read the button

    /*     
    Serial.print(index, DEC);
    Serial.print(": cstate=");
    Serial.print(currentstate[index], DEC);
    Serial.print(", pstate=");
    Serial.print(previousstate[index], DEC);
    Serial.print(", press=");
    */

    if (currentstate[index] == previousstate[index]) {
      if ((pressed[index] == LOW) && (currentstate[index] == LOW)) {
          // just pressed
          justpressed[index] = 1;
      }
      else if ((pressed[index] == HIGH) && (currentstate[index] == HIGH)) {
          // just released
          justreleased[index] = 1;
      }
      pressed[index] = !currentstate[index];  // remember, digital HIGH means NOT pressed
    }
    //Serial.println(pressed[index], DEC);
    previousstate[index] = currentstate[index];   // keep a running tally of the buttons
  }
}

void loop() {
  for (byte i = 0; i < NUMBUTTONS; i++) {
    if (justpressed[i]) {
      justpressed[i] = 0;
      Serial.print(i, DEC);
      Serial.println(" Just pressed");
      // remember, check_switches() will CLEAR the 'just pressed' flag
    }
    if (justreleased[i]) {
      justreleased[i] = 0;
      Serial.print(i, DEC);
      Serial.println(" Just released");
      // remember, check_switches() will CLEAR the 'just pressed' flag
    }
    if (pressed[i]) {
      Serial.print(i, DEC);
      Serial.println(" pressed");
      // is the button pressed down at this moment
    }
  }
}

If you want to make a clock with an Arduino/Boarduino/AVR, there is a way to hook up a precision 32khz watch crystal

mtbf0 shows you how! pictured above is his LCD clockduino!

Trialex followed up with a really-big-7-segment clock (in the same thread)