using System;

using System.Collections.Generic;

​

var text = "abc--b-0t-58-51u9";

var numbers = new List<int>();

​

var isNumber = false;

var isNegative = false;

foreach (var symbol in text)

{

    if (symbol == '-')

    {

        isNegative = true;

        isNumber = false;

    }

    else if (char.IsDigit(symbol))

    {

        var value = symbol - '0';

        if (isNegative)

        {

            value = -value;

        }

​

        if (isNumber)

        {

            numbers[^1] = numbers[^1] * 10 + value;

        }

        else

        {

            numbers.Add(value);

            isNumber = true;

        }

    }

    else

    {

        isNegative = false;

        isNumber = false;

    }

}

​

Console.WriteLine(string.Join(", ", numbers));