How to update existing Font in Windows Forms

In Windows Forms, I have a textbox which I want user to set its font style.

Something like:

   Font font = new Font(textBox1.Font,FontStyle.Regular);
   if (checkBox1.Checked == true)
        font= new Font(font,FontStyle.Bold);
   if (checkBox2.Checked == true)
        font = new Font(font, FontStyle.Italic);
   if (checkBox3.Checked == true)
        font = new Font(font, FontStyle.Underline);
   textBox1.Font = font;

The thing is if two of checkboxes are selected I would have to do like:

font = new Font(font, FontStyle.Italic|FontStyle.Italic);

Then check all possible combinations. Is there a way to define a font then add properties to its style? instead of checking all possible if combinations.

something like:

Font font= new Font();
if (checkBox1.Checked == true)
        font.Bold=true;
   if (checkBox2.Checked == true)
        font.Italic=true;
   if (checkBox3.Checked == true)
        font.Underline=true;

Solution

Fonts are immutable, so you can't change a font once it's created.
What you can do is have a variable to hold the font style, and do something like this:

var fontStyle = FontStyle.Regular;

if (checkBox1.Checked)
    {fontStyle |= FontStyle.Bold;}
if (checkBox2.Checked)
    {fontStyle |= FontStyle.Italic;}
if (checkBox3.Checked)
    {fontStyle |= FontStyle.Underline;}

textBox1.Font = new Font(textBox1.Font, fontStyle);