compressed pubkey version

[FabioCarpi]

How to know when to use version 02 or 03 in a compressed pubkey?

let me explain:
in the bitcoin qt, i type the command dumpprivkey in my address 1Cue...
he gave me the key Kw...
but making some tests, with version 02, i got the address 1Nra...
and with the version 03, the 1Cue...

[amaclin]

How to know when to use version 02 or 03 in a compressed pubkey?

Code:

const QByteArray MyKey32::getPublicKeyClassic ( ) const
{
  quint8 buf [65];
  getPublicKey ( buf );
//buf [0] = 0x04;
  return QByteArray ( (const char*)buf, 65 );
}
//--------------------------------------------------------------
const QByteArray MyKey32::getPublicKeyCompressed ( ) const
{
  quint8 buf [65];
  getPublicKey ( buf );
  buf [0] = 0x02 + ( buf [64] & 1 );
  return QByteArray ( (const char*)buf, 33 );
}

[FabioCarpi]

sry amaclin, i post some info...

[amaclin]

sry amaclin, i post some info...

Public key is a pair [x,y]
if 'y' is even - use 0x02
if 'y' is odd - use 0x03

Code:

buf [0] = 0x02 + ( buf [64] & 1 );