Add One to an Array as a Number in c#

addonetoarrayasno.cs

//Add One to an Array as a Number
//Input           Result
//[1, 3, 2, 4]    [1, 3, 2, 5]
//[1, 4, 8, 9]    [1, 4, 9, 0]
//[9, 9, 9, 9]    [1, 0, 0, 0, 0]

var lst = new List<int> { 1, 4, 8, 9 };
var one = 1;
var revlst = lst.ToArray().Reverse().ToList();

var reslst = new List<int>();
int temp = 0;
int idx = 0;
foreach (var i in revlst)
{
    int addres;
    if (idx ==0)
    {
        addres = i + one;
    }
    else
    {
        addres = i + temp;
    }
    idx++;

    var straddres = addres.ToString();
    if (straddres.Length > 1)
    {
        var lastdigit = straddres.Substring(straddres.Length - 1);
        var remdigits = straddres.Substring(0, straddres.Length - 1);
        temp = int.Parse(remdigits);
        reslst.Add(int.Parse(lastdigit));
    }
    else
    {
        temp = 0;
        reslst.Add(addres);
    }

    if((idx==revlst.Count())&& (temp!=0))
        reslst.Add(temp);

}

var res2 = reslst.ToArray().Reverse().ToList();
foreach(var i in res2)
{
    Console.WriteLine(i);
}

///////////////////////////////////////////////  alternative solution ///////////////////////////////////////


var input = new List<int> { 9, 9, 9, 9 };
var strinput = string.Empty;
input.ForEach(x => strinput = strinput + x);
var intinput = int.Parse(strinput);
var intresult = intinput + 1;
var strresult = intresult.ToString();
var result = new List<int>();
strresult.ToCharArray().ToList().ForEach(x =>
{
result.Add(int.Parse(x.ToString()));
});
result.ForEach(x => Console.WriteLine(x));