Change value integer to currency with decimal

Try handling the textbox's Leave event as follows:

private void textBox1_Leave(object sender, System.EventArgs e)

{

    decimal d;

    Decimal.TryParse(textBox1.Text, out d);

    textBox1.Text = d.ToString("c");

}

The code assumes you're in a culture which uses the $ as its currency. If you're not, then change the last line to:

   textBox1.Text = "$" + d.ToString("c").Substring(1);
    
If the textbox doesn't contain a valid number, this code should set it to $0.00.