C# int 与 string的相互转型

代码:

class Program
    {
        static void Main()
        {
            int a = 123;
            string s1 = a.ToString();
            string s2 = Convert.ToString(a);
            string s3 = ((IConvertible)a).ToString(null);
 9             
            string s = "456";
            int a1 = int.Parse(s);
            int a2 = Convert.ToInt32(s);
            int a3 = ((IConvertible)s).ToInt32(null);
            int a4;
            int.TryParse(s,out a4);
        }
    }