Arduino Mega 2560 with some C - not reading analogue pins

hello everyone,
i facing problem code possibly as, want overclock adcs (for audio recording)
and store samples sram or external module. can not understand keep getting
the value "1023" whether there input or not , can not pretty udnerstand this! should declare want
the analog pins work input? , why not work?  if have questions please let me know.

thank in advance,

napster

code: [select]


int time;

#define fastadc 1

// defines setting , clearing register bits
#ifndef cbi
#define cbi(sfr, bit) (_sfr_byte(sfr) &= ~_bv(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_sfr_byte(sfr) |= _bv(bit))
#endif

void setup() {
  int start ;
  int ;
    serial.begin(9600);
#if fastadc
  // set prescale 2,16,32 etc
  cbi(adcsra,adps2) ;
  cbi(adcsra,adps1) ;
  cbi(adcsra,adps0) ;
#endif
}
void loop() {
  time = micros();
  int sensorvalue = analogread(a0);
  time = micros() - time;
  serial.print("\n");
  serial.println(time);
  serial.print(sensorvalue);
  delay(100);
}


i moron, fogot set pinmode, can done in c , wiring

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