[C#] Enumerate IEnumerable with integer indexes

Enumarate.cs

using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;

class Program {
    static void Main() {
        var PIString = Math.PI.ToString();
        foreach (var (c, i) in PIString.Enumerate())
            WriteLine($"{i + 1, 2}th letter: {c}");
    }
}

static class MyExtensions {
    public static IEnumerable<(T, int)> Enumerate<T>(this IEnumerable<T> source) => source.Select((x, i) => (x, i));
}

Enumerate() function in this code zips an IEnumerable value and the sequence of the natural number.

Result of the execution of the code above: