using System;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {

        const int sLen = 30, Loops = 5000;

        DateTime sTime, eTime;

        int i;

        string sSource = new String('X', sLen);

        string sDest = "";

        // 

        // Time string concatenation.

        // 

        sTime = DateTime.Now;

        for (i = 0; i < Loops; i++)

            sDest += sSource;

        eTime = DateTime.Now;

        Console.WriteLine("Concatenation took " + (eTime - sTime).TotalSeconds + " seconds.");

        // 

        // Time StringBuilder.

        // 

        sTime = DateTime.Now;

        System.Text.StringBuilder sb = new System.Text.StringBuilder((int)(sLen * Loops * 1.1));

        for (i = 0; i < Loops; i++)

            sb.Append(sSource);

        sDest = sb.ToString();

        eTime = DateTime.Now;

        Console.WriteLine("String Builder took " + (eTime - sTime).TotalSeconds + " seconds.");

        // 

        // Make the console window stay open

        // so that you can see the results when running from the IDE.

        // 

        Console.WriteLine();

        Console.Write("Press Enter to finish ... ");

        Console.Read();

    }

}