TextBox.Text saves the text as a simple line, it does not care about the real "value" of the line.
Then, if you want to return your number, you need to parse the string, so neither explicit nor explicit casting to int is allowed (or, better, it will throw an exception if you do this ...).
, UNICODE (UTF-16), , 2 4 ( ).
( - ..), :
int numBytes = Encoding.Unicode.GetByteCount(stringToMeasure);
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