using static System.Console;

using System.Collections.Generic;

using System.Linq;

public class Program {

    public static void Main() {

        var list = new List<int> { 1, 2, 3, 4, 5 };

        foreach (var pair in list.Select((x, i) => new {Index = i, Value = x})) {

            WriteLine($"{pair.Index}: {pair.Value}");

        }

    }

}