C#------stringの共通メンバー関数

			String str1 = "123114511";
			//  
			Console.WriteLine (str1.CompareTo ("11344"));//1
			Console.WriteLine (String.Compare ("123", "345"));//-1
			Console.WriteLine (String.Equals ("2", "3"));//false
			               
			//  
			Console.WriteLine (str1.Insert (2, "abc"));//12abc345
			Console.WriteLine (str1.IndexOf ("34"));//2，    
			Console.WriteLine (str1.Trim ('1'));//          1
			//C#      C++ ，string.at   	,         
			Console.WriteLine (str1 [3]);//2
			Console.WriteLine (str1.StartsWith ("123"));//    123   ，true