string s = "20120819";
 s = s.Insert(4, "年");
 s = s.Insert(7, "月");
 s = s.Insert(10, "日");
 int slen=s.Length ;
 s = s + "    本次字符串总长度为" + slen;
 textBox1.Text = s;

            string s = "20120819";
            s = s.Insert(s.IndexOf("08"), "年");
            s = s.Insert(s.IndexOf("19"), "月");
            s = s+"日";
            int slen=s.Length ;
            s = s + "    本次字符串总长度为" + slen+"***";
            textBox1.Text = s;

.

.

不懂啊 不过还是学习下哈 ，，我去找度娘哈！