Error in the value read from serialPort->bytesAvailable()

[sdcr]

The value read from sp->bytesAvailable() change when I change the while loop condition. Examples:

@@ CONDITION 1 [ == ]

** CODE
// write in serial Port
sp->clear();
sp->write(...);
sp->waitForBytesWritten(100);

// read in serial port
qint64 bites = 0;
spBill->waitForReadyRead(100);

while (((bites = sp->bytesAvailable()) == 0) && (ind < _RETRY))
{
std::cout << "bytes = " << bites << std::endl;
debugShow(QString("Esperando respuesta desde puerto serie. retry %1 de %2..").arg(ind).arg(_RETRY));
sp->waitForReadyRead(100);
ind++;
}

** CONSOLE OUTPUT
bytes = 0
Esperando respuesta desde puerto serie. retry 0 de 100..
bytes = 0
Esperando respuesta desde puerto serie. retry 1 de 100..
bytes = 0
Esperando respuesta desde puerto serie. retry 2 de 100..
bytes = 0
Esperando respuesta desde puerto serie. retry 3 de 100..
..
..
bytes = 0
Esperando respuesta desde puerto serie. retry 100 de 100..

@@ CONDITION 2 [ != 0 ]

** CODE
// write in serial Port
sp->clear();
sp->write(...);
sp->waitForBytesWritten(100);

// read in serial port
qint64 bites = 0;
spBill->waitForReadyRead(100);

while (((bites = sp->bytesAvailable()) != 0) && (ind < _RETRY))
{
std::cout << "bytes = " << bites << std::endl;
debugShow(QString("Esperando respuesta desde puerto serie. retry %1 de %2..").arg(ind).arg(_RETRY));
sp->waitForReadyRead(100);
ind++;
}

** CONSOLE OUTPUT
bytes = 1
Esperando respuesta desde puerto serie. retry 0 de 100..
bytes = 2
Esperando respuesta desde puerto serie. retry 1 de 100..
bytes = 3
Esperando respuesta desde puerto serie. retry 2 de 100..
..
..
bytes = 5
Esperando respuesta desde puerto serie. retry 100 de 100..

Test are made on a device connected to serial port through a serial port adapter on ubuntu.

The value of sp->bytesAvailable() is modified to evaluated the while loop condition always true.. What would be the problem in the code?

thanks

[Jeroen3]

@sdcr said:

(bites = sp->bytesAvailable())

Although it should return a reference to bites, it is not good coding practice imho.
http://en.cppreference.com/w/cpp/language/operator_assignment