//To my knowledge I did this in a simple way
static void Main(string[] args)
{
    string a, b;
    int f1, f2, x, y;
    Console.WriteLine("Enter two inputs");
    a = Convert.ToString(Console.ReadLine());
    b = Console.ReadLine();
    f1 = find(a);
    f2 = find(b);

    if (f1 == 0 && f2 == 0)
    {
        x = Convert.ToInt32(a);
        y = Convert.ToInt32(b);
        Console.WriteLine("Two inputs r number \n so that addition of these text box is= " + (x + y).ToString());
    }
    else
        Console.WriteLine("One or two inputs r string \n so that concatenation of these text box is = " + (a + b));
    Console.ReadKey();
}

static int find(string s)
{
    string s1 = "";
    int f;
    for (int i = 0; i < s.Length; i++)
       for (int j = 0; j <= 9; j++)
       {
           string c = j.ToString();
           if (c[0] == s[i])
           {
               s1 += c[0];
           }
       }

    if (s == s1)
        f = 0;
    else
        f = 1;

    return f;
}

翻倍。TryParse

bool Double.TryParse(string s, out double result)

试试下面定义的正则表达式

new Regex(@"^\d{4}").IsMatch("6")    // false
new Regex(@"^\d{4}").IsMatch("68ab") // false
new Regex(@"^\d{4}").IsMatch("1111abcdefg")
new Regex(@"^\d+").IsMatch("6") // true (any length but at least one digit)

使用这些扩展方法可以清楚地区分检查字符串是数字还是字符串只包含0-9位数字

public static class ExtensionMethods
{
    /// <summary>
    /// Returns true if string could represent a valid number, including decimals and local culture symbols
    /// </summary>
    public static bool IsNumeric(this string s)
    {
        decimal d;
        return decimal.TryParse(s, System.Globalization.NumberStyles.Any, System.Globalization.CultureInfo.CurrentCulture, out d);
    }

    /// <summary>
    /// Returns true only if string is wholy comprised of numerical digits
    /// </summary>
    public static bool IsNumbersOnly(this string s)
    {
        if (s == null || s == string.Empty)
            return false;

        foreach (char c in s)
        {
            if (c < '0' || c > '9') // Avoid using .IsDigit or .IsNumeric as they will return true for other characters
                return false;
        }

        return true;
    }
}

 bool is_number(string str, char delimiter = '.')
    {
        if(str.Length==0) //Empty
        {
            return false;
        }
        bool is_delimetered = false;
        foreach (char c in str)
        {
            if ((c < '0' || c > '9') && (c != delimiter)) //ASCII table check. Not a digit && not delimeter
            {
                return false;
            }
            if (c == delimiter)
            {
                if (is_delimetered) //more than 1 delimiter
                {
                    return false;
                }
                else //first time delimiter
                {
                    is_delimetered = true;
                }
            }
        }
        return true; 
    }

您可以使用TryParse来确定该字符串是否可以解析为整数。

int i;
bool bNum = int.TryParse(str, out i);

布尔值会告诉你它是否有效。