c# RichTextBox 使关键字变色

        private void tSql_TextChanged(object sender, EventArgs e)
        {
            int index = this.tSql.SelectionStart;    //记录修改的位置
            this.tSql.SelectAll();
            this.tSql.SelectionColor = Color.Black;
            
            //SQL关键字
            //string[] keystr ={ "select ", "from ", "where ", " and ", " or ",
            //                   " order ", " by ", " desc ", " when ", " case ",
            //                   " then ", " end ", " on ", " in ", " is ", " else ",
            //                   " left ", " join ", " not ", " null " };

            //C#关键字
            string[] keystr = {
                                  "abstract ", "enum ", "long ", "stackalloc ",
                                  "as ", "event ", "namespace ", "static ",
                                  "base ", "explicit ", "new ", "string ",
                                  "bool ", "extern ", "null ", "struct ",
                                  "break ", "false ", "object ", "switch ",
                                  "byte ", "finally ", "operator ", "this ",
                                  "case ", "fixed ", "out ", "throw ",
                                  "catch ", "for ", "params ", "try ",
                                  "checked ", "foreach ", "private ", "typeof ",
                                  "class ", "goto ", "protected ", "uint ",
                                  "const ", "if ", "public ", "ulong ",
                                  "continue ", "implicit ", "readonly ", "unchecked ",
                                  "decimal ", "in ", "ref ", "unsafe ",
                                  "default ", "int ", "return ", "ushort ",
                                  "delegate ", "interface ", "sbyte ", "using ",
                                  "do ", "internal ", "sealed ", "virtual ",
                                  "double ", "is ", "short ", "void ",
                                  "else ", "lock ", "sizeof ", "while "
                              };

            for (int i = 0; i < keystr.Length; i++)
                this.getbunch(keystr[i], this.tSql.Text);

            this.tSql.Select(index, 0);     //返回修改的位置
            this.tSql.SelectionColor = Color.Black;
        }

        public int getbunch(string p, string s)  //给关键字上色
        {
            int cnt = 0;
            int M = p.Length;
            int N = s.Length;
            char[] ss = s.ToCharArray(), pp = p.ToCharArray();
            if (M > N) return 0;
            for (int i = 0; i < N - M + 1; i++)
            {
                int j;
                for (j = 0; j < M; j++)
                {
                    if (ss[i + j] != pp[j]) break;
                }
                if (j == p.Length)
                {
                    this.tSql.Select(i, p.Length);
                    this.tSql.SelectionColor = Color.Blue;
                    cnt++;
                }
            }
            return cnt;
        }