程序代码：

        /// <summary>
        /// 选中行
        /// </summary>
        /// <param name="line">行号,从0开始</param>
        private void selectLine(int line)
        {
            int a = this.richTextBox1.GetFirstCharIndexFromLine(line);
            int b = this.richTextBox1.GetFirstCharIndexFromLine(++line);
            if (a == -1)
                return;
            else if (b == -1)
                b = this.richTextBox1.TextLength - a;
            else
                b = b - a;
            this.richTextBox1.Select(a, b);
        }