C#

//Two arrays
string[] arrayOne = new string[]{"Hello", "World"};
string[] arrayTwo = new string[]{"Have", "a", "nice", "day"};

//Length of both together
int newArrayLength = arrayOne.Length + arrayTwo.Length;

//Set first to variable
string[] arrayThree = arrayOne;

//resize first to sum of lengths
arrayOne = new String[newArrayLength];

//Add values from first (now held in temp variable)
int iterator = 0;
foreach(string s in arrayThree)
{
        arrayOne[iterator] = s;
	iterator++;
}

//Add values from second
foreach(string s in arrayTwo)
{
	arrayOne[iterator] = s;
	iterator++;
}

using System.Collections;

// stuff omitted
ArrayList array1 = new ArrayList();
array1.Add("hello");
array1.Add("world");
ArrayList array2 = new ArrayList();
array2.Add("Bonjour");
array2.Add("le monde");
array1.AddRange( array2 );

"hello",
"world",
"Bonjour",
"le monde"

public class MyThingy {

    private bool testConnectionComplete = false;
    private bool testConnectionResult = false;

    ....

    public override void Form_Load(...) {
       Thread tcStart = new Thread(new ThreadStart(this.TestConnection));
       tcStart.Start();
       Thread tcMonitor = new Thread(new ThreadStart(this.CheckTestConnection));
       tcMonitor.Start();
    }

    public void TestConnection() {
       // do connection stuff
       this.testConnectionResult = WhateverYourResultIs;
       this.testConnectionComplete = true;
    }

    public void CheckTestConnection() {
       while( this.testConnectionComplete == false ) {
          // sleep, hang out, do nothing, etc.
       }
       // Your testConnectionResult is valid now. Do your messagebox thingy
    }
}