using System.Text.RegularExpressions;

string a = "";

string b = "";

string c = "";

string d = "";

int max1 = 0;

int max2 = 0;

int max = 0;

a = Console.ReadLine();

while (!IsNum(a))

{

Console.WriteLine("非數字,請重新輸入。");

a = Console.ReadLine();

}

b = Console.ReadLine();

while (!IsNum(b))

{

Console.WriteLine("非數字,請重新輸入。");

b = Console.ReadLine();

}

c = Console.ReadLine();

while (!IsNum(c))

{

Console.WriteLine("非數字,請重新輸入。");

c = Console.ReadLine();

}

d = Console.ReadLine();

while (!IsNum(d))

{

Console.WriteLine("非數字,請重新輸入。");

d = Console.ReadLine();

}

max1 = Convert.ToInt32(a) > Convert.ToInt32(b) ? Convert.ToInt32(a) : Convert.ToInt32(b);

max2 = Convert.ToInt32(c) > Convert.ToInt32(d) ? Convert.ToInt32(c) : Convert.ToInt32(d);

max = max1 > max2 ? max1 : max2;

Console.WriteLine("最大數是：{0}", max);

Console.WriteLine("按任意鍵退出!");

Console.ReadLine();

}

public static bool IsNum(string s)

{

return Regex.IsMatch(s, @"^\d+");

}

記事本寫的..未測試...