Reading from text file, return the output of my function in a textbox

[Greenwood]

Im writting a program which read a file choosen by the user, it is a txt. file with some numbers in it like :
98.09809
09.9879
95.35445
after the file has been read, I do some mathematical calculation, the one Im doing here is the standard deviation of all the data in the file. But
my problem is that I return the result of the function and try to output it to a textbox, nothing worked my textbox is empty. Please advise. here is my code!

namespace test
{
    public partial class Form1 : Form
    {
        List<double> dataValues = new List<double>();
           
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void ouvrirToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (ofd.ShowDialog(this) == DialogResult.OK)
            {
                FileStream fs = new FileStream(ofd.FileName, FileMode.Open);
                StreamReader sr = new StreamReader(fs);
                String nbr;

                while ((nbr = sr.ReadLine()) != null)
                {
                    double data = 0.0;
                    if ((double.TryParse(nbr, out data)))
                        dataValues.Add(data);
                        //textBox1.Text += nbr.ToString() + "\r\n";
                           //Console.WriteLine(data);  
                }
                sr.Close();
                fs.Close();       
            }
        }
        
        public double std(List<double> dataValues)
        {
            double average = 0.0;

            foreach (double d in dataValues)
            {
                average += d;
            }

            average /= (double)dataValues.Count;

            //Calculate standard deviation
            List<double> stdDev = new List<double>();
            foreach (double d in dataValues)
            {
                stdDev.Add(Math.Pow((d - average), 2));
            }

            //Sum of all values, divide by the average and take sqrt to get std
            double standardDeviation = Math.Sqrt((stdDev.Sum() / average));

              return standardDeviation;
              
              textBox1.Text += string.Format("{0}", standardDeviation);
              //textBox1.Text += standardDeviation.ToString();
              
        }

        
        
        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }
        
        }
 }

[marcellus7]

You have to set the Standard Deviation to the text box field before you return Standard Deviation, because when it returns it will exit the function;

Or when you call the std function you can set it to the textbox value like:

[code]textBox1.Text+= CStr(std(List)) ;