void AddCh()
{
if (tlen >= tval.Length) {
char[] newBuf = new char[2 * tval.Length];
Array.Copy(tval, 0, newBuf, 0, tval.Length);
tval = newBuf;
}
if (ch != Buffer.EOF) {
tval[tlen++] = (char) ch;
NextCh();
}
}