using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string A = "12345678abcdefghijklmn";

        string B = "22345678abcdefghijjlmn";

        var diffs = A.Zip(B).Select((pair, idx) => (pair, idx))

                     .Where(val => char.ToLower(val.pair.First) != char.ToLower(val.pair.Second));

        var ranges = new List<(string item, int begin, int end)>

            { ("項目A", 0, 8), ("項目B", 0, 2), ("項目C", 8, 8+13+1) };

​

        ranges.ForEach(r => {

            var included = diffs.Where(val => r.begin <= val.idx && val.idx < r.end);

            if (!included.Any()) return;

            Console.WriteLine($"{r.item}, 比較文字列A:{A[r.begin..r.end]}, 比較文字列B:{B[r.begin..r.end]}");

            foreach (var i in included)

                Console.WriteLine($"不一致箇所:{i.idx-r.begin+1}, 不一致文字A:{i.pair.First}, 不一致文字B:{i.pair.Second}");

            Console.WriteLine();

        });     

    }

}