how to do two different functions with a textbox

if(textBox1.Text == File.ReadAllLines(@"C:/database.txt")//if your textbox has a line from database...
{
     MessageBox.Show("One match found: " + textBox1.Text); //Show messageBox

}else //if the textbox has no match with a line from database...
     {
     MessageBox.Show("No match found! Added to database instead."); //Show messageBox
     StreamWriter sw = new StreamWriter(@"C:/database.txt"); //Create StreamWriter to modify database
     sw.WriteLine(textBox1.Text); //Add the new value to database
     sw.Close(); //Close the streamWriter
}