验证用户名不为空并且不存在

using System;
using System.Globalization;
using System.Linq.Expressions;

class Program
{
    public static void Main(string[] args)
    {
        var oneName = "";
        var twoName = "";
        while (true)
        {
            oneName = GetString();
            if (oneName.Trim() != "")
            {
                break;
            }
            else
            {
                Print("用户名不能为空!");
            }
        }
        while (true)
        {
            twoName = GetString().Trim();
            if (twoName != "" && twoName != oneName)
            {
                break;
            }else if (twoName=="")
            {
                Print("用户名不能为空!");
            }
            else
            {
                Print("用户名不能相同");
            }
        }
        Print(oneName);
        Print(twoName);
    } //Main函数结束


    #region 工具方法

    public static void Print(string obj, params object[] arg)
    {
        Console.WriteLine(obj, arg);
    }

    public static void Print(object obj)
    {
        Console.WriteLine(obj);
    }

    /// <summary>
    /// 获得一个int类型的值
    /// </summary>
    /// <returns></returns>
    public static int GetInt()
    {
        int i;
        while (true)
        {
            try
            {
                i = Convert.ToInt32(Console.ReadLine());
                break;
            }
            catch (FormatException e)
            {
                Console.WriteLine(e.Message);
            }
        }
        return i;
    }

    public static string GetString()
    {
        return Console.ReadLine();
    }

    public static double GetDouble()
    {
        double i;
        while (true)
        {
            try
            {
                i = Convert.ToDouble(Console.ReadLine());
                break;
            }
            catch (FormatException e)
            {
                Console.WriteLine(e.Message);
            }
        }
        return i;
    }

    #endregion
}