c#字符串自动补齐空格的问题

求高手给个好的解决办法。                                                  C#                                              
[解决办法]
引用:
String.PadLeft("",30)

写反了
 string pad = "dada";
            pad = pad.PadLeft(30);
[解决办法]
pad = pad.PadLeft(30); 这个应该能满足要求！
[解决办法]
 string str = "==";
                int num = 30;
                int left = (num - str.Length) / 2;
                str = str.PadLeft(left, ' ').PadRight(num, ' ');

[解决办法]
        public static void Main()
        {
            string[] test = {"hello", "hi", "this is a test"};

            test.ToList().ForEach(str => Console.WriteLine( ConvertStringTo30(str)));

            Console.ReadKey();
        }

        public static string ConvertStringTo30(string src)
        {
            if(src.Length> 30)
                throw new ArgumentOutOfRangeException("String is longer than 30");

            var sb = new StringBuilder();
            sb.Append('=', (30 - src.Length) / 2); 
 
            sb.Append(src);
            sb.Append('=', 30 - sb.Length);

            return sb.ToString();
        }

输出：
============hello=============
==============hi==============
========this is a test========