C#

StreamWriter writer = new StreamWriter (existingFilePath);
StreamReader reader = new StreamReader(copiedFilePath);

byte[] buffer = new byte[32768];    
while (true)    {        
     int read = reader.Read (buffer, 0, buffer.Length);\
     if (read <= 0)            
          break;   // <--- EDITED: IT WAS return
     writer.Write (buffer, 0, read);    
}

writer .Close();
reader.Close();

while  (reader.Read (buffer, 0, buffer.Length) > 0 )    {        
     writer.Write (buffer, 0, read);    
}

int read = 0;
while  ((read = reader.Read (buffer, 0, buffer.Length)) > 0 )    {        
     writer.Write (buffer, 0, read);    
}
if (read < buffer.Length) {
   //do whatever 
}

riced wrote:

It isn't and does not need to be unless you want to compare the number of bytes read with size of buffer