String类

            //String    Math
            string a = " aldsfdh  ";
            //bool q = a.Contains("dd");//是否包含此字符串

            int o = a.IndexOf("h");
            Console.WriteLine(o);
            int p = a.LastIndexOf("d");
            Console.WriteLine(p);

            int b = a.Length;//长度
            Console.WriteLine(b);
            string c = a.Trim();//去掉前后空格
            Console.Write(c);

            string d = a.TrimStart();//去掉前空格
            Console.Write(d);

            string e = a.TrimEnd();//去掉后空格
            Console.Write(e);

            string f = a.ToUpper();//全部将小写字母转换为大写
            Console.Write(f);

            string g = a.ToLower();//全部将大写字母转换为小写
            Console.Write(g);

            //索引是从0开始的
            string h = a.Substring(4);//里面一个值，表示从这个索引值开始一直截取到最后
            Console.WriteLine(h);
            Console.WriteLine(a.Substring(8));//a=a.Substring(8);//若不重新赋值，a无变化

            string i = a.Substring(4, 3);
            Console.WriteLine(i);

            a = a.Replace("de", "DE");
            Console.WriteLine(a);

            string j = "2012/12/23";
            string[] aa = j.Split();//分割字符串，

判断邮箱格式是否正确