csharp convert random numbers in textBox to currency

                
                        public void textchange(object sender, EventArgs e)
{
   if(textbox1.Text.Contains("%%%~COMPRESS~PRE~0~%%%quot;))
   {
     string valueToConvert = textbox1.Text.replace("%%%~COMPRESS~PRE~0~%%%quot;,"");
     double newVal = Convert.ToDouble(valueToConvert);

     //Assign the new value with $ to textbox1
     textbox1.Text = "%%%~COMPRESS~PRE~0~%%%quot;+Convert.ToString(newVal);
   }
}