DECLARE @Result varchar(4000)
SET @Result = LTRIM(RTRIM(REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(@InputString, CHAR(9), ''), CHAR(10), ''), CHAR(13), ''), CHAR(31), ''), CHAR(1), '')))
RETURN @Result

IF (@Result = '')
RETURN NULL

public static class MyString {
        public static String MyReplace(this string input, char[] oldChar, char newChar) {
            foreach (var c in oldChar) {
                input = input.Replace(c, newChar);
            }
            return input;
        }
    }

private void button1_Click(object sender, EventArgs e) {
            char[] arr = new char[3]{'2','3','4'};
            var str = textBox1.Text;
            textBox1.Text += str.MyReplace(arr, 'W');
        }