program.cs

using System;
using System.Diagnostics;

namespace kata.App
{
    class Program
    {
        static void Main(string[] args)
        {
            string line;
            int number = 0;
            bool first = true;
            System.IO.StreamReader file =
                new System.IO.StreamReader("/home/yolan/RiderProjects/kata/src/kata.App/numbers.txt");
            System.Console.Write("Enter '+' or '*': ");
            string op = Console.ReadLine();

            while ((line = file.ReadLine()) != null)
            {
                if (op.Equals("*")) number = first ? Int32.Parse(line) : Int32.Parse(line) * number;
                else number = first ? Int32.Parse(line) : Int32.Parse(line) + number;
                if (first)
                {
                    System.Console.WriteLine(line);
                    first = false;
                }
                else
                {
                    if (op.Equals("*")) System.Console.WriteLine("*{0} (={1})", line, number);
                    else System.Console.WriteLine("+{0} (={1})", line, number);
                }
            }

            file.Close();

            if (op.Equals("*"))
                System.Console.WriteLine("-------\n" +
                                         "total = {0} (multiplication)", number);
            else
                System.Console.WriteLine("-------\n" +
                                         "total = {0} (addition)", number);
        }
    }
}