sd卡放音乐 用库文件 ，不用电脑控制求建议，帮忙想想怎样随机播放

渲染♀离别^

这个是代码，谁能一起想想自动循环的语法，（我是用if来选择，也可以用switch，但是如果有几百首个if码子都码死，求简略的方法。。。比方说吧中间的数字用变量来代替，但是我不会==）（原谅我就玩了4天的菜鸟。。）还有很多教程都有具体的电路图，我就不介绍了==。
二号引脚是下一首歌，我还没想到方法让它一首歌放完自动下一首，只能这样==二号引脚是下一首歌，我还没想到方法让它一首歌放完自动下一首，只能这样==
谢谢各位大神帮忙==
#include <SimpleSDAudio.h>

void DirCallback(char *buf) {
  Serial.println(buf);
}

#define BIGBUFSIZE (2*512)
uint8_t bigbuf[BIGBUFSIZE];

// helper function to determine free ram at runtime
int freeRam () {
  extern int __heap_start, *__brkval;
  int v;
  return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
}

void setup()
{
pinMode(2, OUTPUT);
  Serial.begin(9600);
   while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }
  
  Serial.print(F("Free Ram: "));
  Serial.println(freeRam());
  
  // Setting the buffer manually for more flexibility
  SdPlay.setWorkBuffer(bigbuf, BIGBUFSIZE);
  
  Serial.print(F("\nInitializing SimpleSDAudio V" SSDA_VERSIONSTRING " ..."));  
  
  // If your SD card CS-Pin is not at Pin 4, enable and adapt the following line:
  //SdPlay.setSDCSPin(10);
  
  // Select between SSDA_MODE_FULLRATE or SSDA_MODE_HALFRATE (62.5kHz or 31.25kHz)
  // and the output modes SSDA_MODE_MONO_BRIDGE, SSDA_MODE_MONO or SSDA_MODE_STEREO
  if (!SdPlay.init(SSDA_MODE_FULLRATE | SSDA_MODE_MONO | SSDA_MODE_AUTOWORKER)) {
    Serial.println(F("initialization failed. Things to check:"));
    Serial.println(F("* is a card is inserted?"));
    Serial.println(F("* Is your wiring correct?"));
    Serial.println(F("* maybe you need to change the chipSelect pin to match your shield or module?"));
    Serial.print(F("Error code: "));
    Serial.println(SdPlay.getLastError());
    while(1);
  } else {
    Serial.println(F("Wiring is correct and a card is present."));
  }
  

}
int a=0;
char * AudioFileName="(7)~1.AFM";
void loop(void) {
  uint8_t count=0, c, flag;
  
  a=a+1;
   if (a==1)
   {
  AudioFileName="(6)~1.AFM";
};
   if (a==2)
   {
  AudioFileName="(7)~1.AFM";
};
  if (a==3)
   {
  AudioFileName="(8)~1.AFM";
};
  if (a==4)
   {
  AudioFileName="(9)~1.AFM";
};
  if (a==5)
   {
  AudioFileName="(10)~1.AFM";
};

  Serial.println(F("Files on card:"));
  SdPlay.dir(&DirCallback);

  Serial.print(F("Looking for file... "));
SdPlay.setFile(AudioFileName);
Serial.print(AudioFileName);
    flag = 1;
  int i=1;
   
  while(flag) {
    SdPlay.worker();
    if (i==1){
               SdPlay.play();
           Serial.println(F("Play."));
           i=2;      
    }
int a =digitalRead(2);
if (a==HIGH)
{
break;
}

  };
}