value_check C#

public static double Value_check()
{
    bool was_point = false;
    string check = System.Console.ReadLine();
    for (int i = 0; i < check.Length; i++)
    {
        if (check[i] == '.' || check[i] == ',' && !was_point)
        {
            check = check.Remove(i, 1);
            check = check.Insert(i, ",");
            was_point = true;
        }
        else if (check[i] == '.' || check[i] == ',' && was_point)
        {
            check = check.Remove(i, 1);
            i--;
        }
        if ((check[i] < 48 && check[i] != 43 && check[i] != 44 && check[i] != 45 && check[i] != 0) || check[i] > 57)
        {
            check = check.Remove(i, 1);
            i--;
        }
    }
    if (check.Length == 0)
    {
        return 0;
    }
    return System.Convert.ToDouble(check);
}