将文本从2个列表框添加到一个列表框

Question

How can I add items from 2 listBox to one listBox?

ex: listBox1 contain Hello listBox2 contain World! So if button1 is clicked in listbox3 will display Hello World! side bye side but not in a new line like

Hello

World!

private void button2_Click(object sender, EventArgs e)
{
  listBox3.Items.Add(listBox1.Items + listBox2.Items);
}

Answer 1

private void button2_Click(object sender, EventArgs e)
{
  listBox3.Items.Add(string.Format("{0} {1}", listBox1.Items[0].ToString().Trim() , listBox2.Items[0].ToString().Trim()));
}

if you need all words in two list box to a one list box

private void button2_Click(object sender, EventArgs e)
{
  listBox3.Items.Add( string.Format("{0} {1}", string.Join(" ", listBox1.Items.Cast<string>()) , string.Join(" ", listBox2.Items.Cast<string>())));
}

Update :

private void button2_Click(object sender, EventArgs e)
{
  listBox3.Items.AddRange(listBox1.Items.Cast<string>().Zip(listBox2.Items.Cast<string>(), (first, second) => first + " " + second).ToArray());
}

Answer 2

Since you said;

all words in listBox1 will be + with listBox2 in listBox3

private void button2_Click(object sender, EventArgs e)
{
  string s = "";
  for(int i = 0; i < listBox1.Items.Count; i++)
  {
      s += listBox1.Items[i].ToString() + " ";
  }

  for(int j = 0; j < listBox2.Items.Count; j++)
  {
      s += listBox2.Items[j].ToString() + " ";
  }

  listBox3.Items.Add(s.Trim());
}

but ex:my listBox1 contain Hello Hi Sup and my listBox2 contain World! after click in listBox3 it will become Hello Hi Sup World! instead of Hello World! Hi World! Sup World!

If you want as a one item in your listBox3 , you can use upper solution. If you want as total 4 item in your listBox3 , you can use it like;

private void button2_Click(object sender, EventArgs e)
{

  for(int i = 0; i < listBox1.Items.Count; i++)
  {
      listBox3.Items.Add(listBox1.Items[i].ToString());
  }

  for(int j = 0; j < listBox2.Items.Count; j++)
  {
      listBox3.Items.Add(listBox2.Items[j].ToString());
  }

}