How do you use if (IsPostBack) in ASP.NET C#

Question

How can I used if (IsPostBack){} to display user's names from two text boxes into another text box?

I have 3 text boxes and a button. The text boxes are named txtLastName, txtGivenName, txtOutput. My button is btnSubmit.

How can I display text from the txtLastName and txtGivenName in the txtOutput text box?

How can I display it as: First (space) Lastname or Last, Firstname in this code.

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
    }
}

Answer 1

Create an event handler for the Click event on the button and then in the code behind, do like this:

protected void btnSubmit_Click(object sender, EventArgs e)
{
    txtOutput.Text = string.Format("{0} {1}", txtGivenName.Text, txtLastName.Text);
}