using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var texto = "Abcc111de12234";

        var lista = new char[texto.Length];

        for (int i = 0, j = 0; i < texto.Length; i++) 

            if (char.IsDigit(texto[i])) 

                lista[j++] = texto[i];

        var saida = new string(lista);

        var saida2 = new string(texto.Where(c => char.IsDigit(c)).ToArray());

        Console.WriteLine("saida = " + saida);

        Console.WriteLine("saida2 = " + saida2);

    }

}