use one push button with mp3 shield

The project is to use one push button to make a sparkfun mp3 shield cycle through tracks one at a time. I was wondering if anyone had any ideas on how to do this or the direction that I could go. I have tried a few different options, and am now doubting the possibility of it working. This is the code I have been working with. The problem I think I am having is that the source code requires a 0 before the track number but I don’t know how to get that padded 0 there from the bush button.

#include <SPI.h> //bus SPI
#include <SdFat.h> //SD card
#include <SdFatUtil.h> //SD card tools
#include <SFEMP3Shield.h> //shield library

SFEMP3Shield MP3player; //player
SdFat sd; //card
const int pinButton = 5;
const int nbTracks = 5; //CHANGE THIS VALUE TO THE NUMBER OF SONGS ON YOUR SD CARD
const int volume = 2;//-3dB. The higher number, the lower volume
int counter = 01;

void setup() {
  Serial.begin(9600);
  sd.begin(SD_SEL, SPI_HALF_SPEED); //start card 
  pinMode(pinButton, INPUT);
 
  //setup of player
  MP3player.begin(); //start player
  MP3player.setDifferentialOutput(1); //higher output power
  MP3player.setVolume(volume, volume);
}

void loop(){
  if (MP3player.isPlaying() && digitalRead(pinButton)){
    //if playing, then a press of the button stops the music
    MP3player.stopTrack();
    Serial.println("music stopped");
    delay(500); //to release button         
  }
 
  else if(!MP3player.isPlaying() && digitalRead(pinButton)){  
    //if not playing, then a press of the button starts the music
   
    //first, increment counter
    counter += 1;
    if (counter > nbTracks)
    counter = 1;
   
    int errorCode; //used to debug
    errorCode = MP3player.playTrack(counter); //play

      Serial.print("playing track ");     
      Serial.print(counter);
      Serial.print(" at ");    
      Serial.print(-volume/2);
      Serial.println("dB");     
      Serial.print("error code (0 is OK): ");
      Serial.println(errorCode);



     delay(500); //to release button 
  }     
}

Cross post to Programming Forum

Here: http://forum.arduino.cc/index.php?topic=361153.0