Analogue pins not working

hi all,

i complete newbie @ arduino programming, have urgent issue. have built electronic xylophone uses piezo sensors , adrunio mega 2560 detect when note struck , generate midi output. analogue pins a0-a7 seem work, pins a8-a15 not. sensors work when plugged a0-a7. i'm using hairless serial bridge transform serial out midi output. hairless recognises input a0-a7, not a8-a15. code below. appreciated.

int pinread;
char pinassignments[16] ={
  'a0','a1','a2','a3','a4','a5','a6','a7','a8','a9','a10','a11','a12','a13','a14','a15'};
byte padnote[16] = {
  57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72};         // midi notes 0 127 (mid c = 60)
int padcutoff[16] =
{
  100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100};           // minimum analog value cause drum hit
int maxplaytime[16] = {
  90,90,90,90,90,90,90,90,90,90,90,90,90,90,90,90};               // cycles before 2nd hit allowed
#define  midichannel 1;                              // midi channel 0 15 (+1 in "real world")
boolean velocityflag  = true;                           // velocity on (true) or off (false)

//*******************************************************************************************************************
// internal use variables
//*******************************************************************************************************************
boolean activepad[16] = {
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};                   // array of flags of pad playing
int pinplaytime[16] = {
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};                     // counter since pad started play
byte status1;

int pin = 0;     
int hitavg = 0;
//*******************************************************************************************************************
// setup
//*******************************************************************************************************************
void setup()
{
                                 
  serial.begin(115200);

}
//*******************************************************************************************************************
// main program
//*******************************************************************************************************************
void loop()
{
  for(int pin=0; pin < 16; pin++)                          //
  {
    //int pin = 3;
    //   for (pinread=0; pinread < 16, pin++){
    hitavg = analogread(pinassignments[pin]); 
    //serial.println(hitavg);   
    // read input pin

    if((hitavg > padcutoff[pin]))
    {
      if((activepad[pin] == false))
      {
        if(velocityflag == true)
        {
          //          hitavg = 127 / ((1023 - padcutoff[pin]) / (hitavg - padcutoff[pin]));    // full range (too sensitive ?)
          hitavg = (hitavg / -1 ;                                                 // upper range
        }
        else
        {
          hitavg = 127;
        }
        midi_tx(144,padnote[pin],hitavg); //note on

        pinplaytime[pin] = 0;
        activepad[pin] = true;
      }
      else
      {
        pinplaytime[pin] = pinplaytime[pin] + 1;
      }
    }
    else if((activepad[pin] == true))
    {
      pinplaytime[pin] = pinplaytime[pin] + 1;
      if(pinplaytime[pin] > maxplaytime[pin])
      {
        activepad[pin] = false;
        midi_tx(144,padnote[pin],0);
      }
    }
  }
}

//*******************************************************************************************************************
// transmit midi message
//*******************************************************************************************************************
void midi_tx(byte message, byte pitch, byte velocity)
{
  status1 = message + midichannel;
  serial.write(status1);
  serial.write(pitch);
  serial.write(velocity);

}

please modify post, select code part , press # button above smileys. becomes more readable way.

can tell more sensors?  - datasheet link?
what voltage generate?
can tell how did connect sensors? need pull up/down resistor?

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