I am making a calculator to better understand how to program and I had a question about the following lines of code:

I wanted to make my equals sign with this C# code:

private void btnEquals_Click(object sender, EventArgs e)
    {
        if (plusButtonClicked == true)
        {
            total2 = total1 + Convert.ToDouble(txtDisplay.Text);
                //double.Parse(txtDisplay.Text);
        }

        else if (minusButtonClicked == 
            {
            total2 = total1 - double.Parse(txtDisplay.Text)
            }
        }
        txtDisplay.Text = total2.ToString();
        total1 = 0;

However, my friend said this way of writing code was superior, with changes in the minus sign.

private void btnEquals_Click(object sender, EventArgs e)
    {
        if (plusButtonClicked == true)
        {
            total2 = total1 + Convert.ToDouble(txtDisplay.Text);
                //double.Parse(txtDisplay.Text);
        }

        else if (minusButtonClicked == true)
        {
            double d1;
            if(double.TryParse(txtDisplay.Text, out d1))
            {
            total2 = total1 - d1;
            }
        }
        txtDisplay.Text = total2.ToString();
        total1 = 0;

My questions: 1) What does the "out d1" section of this minus sign code mean? 2) My assumption here is that the "TryParse" code results in fewer systems crashes? If I just use "Double.Parse" and I don't put anything in the textbox, the program will crash sometimes right?