C# Output only appear one digit [closed]

I am trying to do a simple code by using break statement. Supposedly, the output should be "1,2,3" but when I run it, the output shows only "3". I have no idea :(

public Form1()
{
    InitializeComponent();
}

private void button9_Click(object sender, EventArgs e)
{
    listBox2.Items.Clear();
    listBox2.Items.Add("for (int num = 0; num < 10; num++)");
    listBox2.Items.Add("{");
    listBox2.Items.Add("   if (num == 4)");
    listBox2.Items.Add("      break;");
    listBox2.Items.Add("}");

    for (int num = 0; num < 10; num++)
    {
        if (num == 4)
         {
            break;
         }
        listBox1.Items.Clear();
        listBox1.Items.Add(num);
    }
}

Output for my code