Get length with s.length() or equivalently s.size(). Both return character count as unsigned integer. The two methods are identical for strings; use whichever reads better. Length counts characters, not bytes.
For ASCII, characters and bytes match. For Unicode with multi-byte characters, it's more complex, but length() returns character count for common uses. Use length for loop bounds: for (int i = 0; i < s.length(); i++).
Check if string has content before processing. Validate input length against minimum or maximum requirements.