Does string contain only digits, C#

Does string contain only digits

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            String str = "1234657k9";
            Boolean flag = DoesStringContainOnlyDigits(str);
            Console.WriteLine("Only digits " + flag);
        }
        
        public static Boolean DoesStringContainOnlyDigits(String st)
        {
            Boolean flag = true;
            foreach(char ch in st)
            {
                if(ch>='0' && ch <= '9')
                    flag = true;
                else
                {
                    flag = false;
                    break;
                }
            }
            
            if(flag)
                return true;
            else
                return false;
        }
    }
}


run \| edit \| history \| help	0