c#用for语句输出一个三角形的方法

using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication1
{
  class Program
  {
    static void Main(string[] args)
    {
      Render(19);
      Console.Read();
    }
    static void Render(int rowNum)
    {
      if (rowNum <= 0 || !System.Text.RegularExpressions.Regex.IsMatch(rowNum.ToString(),@"^\d+$"))
        return;
      int tmpRow = 0;
      for (int i = 1; i <= rowNum; i++)
      {
        //对称输出
        tmpRow = i <= rowNum / 2 ? i : rowNum - i + 1;
        Console.WriteLine("{0}", new string('*', 2 * tmpRow - 1));
      }
    }
  }
}