How to Make a DIY Music Player?

/*
*  name:     DFPlayer_Mini_Mp3
*  version:  1.0
*  Author:   Apple tec.<[email][email protected][/email]>
*  Date:     2015-07-16
*  Description:  
*  note: mp3 file must put into mp3 folder in your tf card
*/

#include 
#include 
#include 

//定义对应16进制数值的常量名
#define POWER   0xFD00FF       
#define VOLUP   0xFD807F       //VOL+
#define STOP    0xFD40BF       //FUNC/STOP
#define PREV    0xFD20DF      
#define PAUSE   0xFDA05F       
#define NEXT    0xFD609F     
#define DOWN    0xFD10EF   
#define VOLDOWN 0xFD906F       //VOL-
#define UP      0xFD50AF     
#define ZERO    0xFD30CF       //0
#define EQ      0xFDB04F       //EQ
#define REPT    0xFD708F       //ST/REPT
#define ONE     0xFD08F7       //1
#define TWO     0xFD8877       //2
#define THREE   0xFD48B7       //3
#define FOUR    0xFD28D7       //4
#define FIVE    0xFDA857       //5
#define SIX     0xFD6897       //6
#define SEVEN   0xFD18E7       //7
#define EIGHT   0xFD9867       //8
#define NINE    0xFD58A7       //9

int recvPin = 2;             
boolean a = true;             
int i = 20;                  
int z = 0;                   
IRrecv recv(recvPin);        
decode_results res;         

void setup() {
  Serial.begin(9600);          
  recv.enableIRIn();           
  mp3_set_serial (Serial);      
  mp3_set_volume (i);         
  mp3_set_EQ (z);              
}

void loop() {
  if(recv.decode(&res)) {                        
    switch(res.value) {                          

      case POWER:                               
      if (a == false) {
        a = !a;
        mp3_stop ();
        }
      break;

      case PREV:                                
      if (a == true) {
        a = !a;
        }
      mp3_prev ();
      break;

      case NEXT:                                
      if (a == true) {
        a = !a;
        }
      mp3_next ();
      break;

      case PAUSE:                               
      if (a == true) {
        a = !a;
        mp3_play ();
        }
      else { 
        a = !a;
        mp3_pause ();
        }
      break;

      case VOLUP:                                
      if (i < 30) {
        i = i+1;
        mp3_set_volume (i);
        }
      break;

      case VOLDOWN:                              
      if (i > 0) {
        i = i-1;
        mp3_set_volume (i);
        }
      break;

      case EQ:                                 
      if (z < 5) {
        z = z+1;
        }
      else {
        z = 0;
        }
      mp3_set_EQ (z);
      break;

      case REPT :                                
      if (a == true) {
        a = !a;
        }
      mp3_random_play (); 
      break;

      case ONE:
      if (a == true) {
        a = !a;
        }
      mp3_play (1);
      break;

      case TWO:
      if (a == true) {
        a = !a;
        }
      mp3_play (2);
      break;

      case THREE:
      if (a == true) {
        a = !a;
        }
      mp3_play (3);
      break;

      case FOUR:
      if (a == true) {
        a = !a;
        }
      mp3_play (4);
      break;

      case FIVE:
      if (a == true) {
        a = !a;
        }
      mp3_play (5);
      break;

      case SIX:
      if (a == true) {
        a = !a;
        }
      mp3_play (6);
      break;

      case SEVEN:
      if (a == true) {
        a = !a;
        }
      mp3_play (7);
      break;

      case EIGHT:
      if (a == true) {
        a = !a;
        }
      mp3_play (8);
      break;

      case NINE:
      if (a == true) {
        a = !a;
        }
      mp3_play (9);
      break;

      default:
      ;
      }
      recv.resume();                           
    }
}