c# how do I use a method in a Windows Forms App?

Question

I am new to c# and I just need something basic. I am trying to call a method from a button click and I don't know if I declare an object and method in Program.cs or Form1.cs

Here is what I have so far.

    public partial class frmMain : Form
{
    Form form = new Form();

    public frmMain()
    {
        InitializeComponent();
    }

    private void btnCalc_Click(object sender, EventArgs e)
    {
        txtC.Text = form.CalcHypotenuse(double.Parse(txtA.Text), double.Parse(txtB.Text));
    }

}

public string CalcHypotenuse(double sideA, double sideB)
{
    double hypotenuse = Math.Sqrt((sideA * sideA) + (sideB * sideB));
    string hypotenuseString = hypotenuse.ToString();
    return hypotenuseString;
}

Answer 1

Methods need to be inside a class. Your form is a class so just put the method inside it and then you can call it. Please note I have moved the method inside the frmMain class and removed the line Form form = new Form(); since you do not need it.

public partial class frmMain : Form
{    
    public frmMain()
    {
        InitializeComponent();
    }

    private void btnCalc_Click(object sender, EventArgs e)
    {
        // the 'this' is optional so you can remove it
        txtC.Text = this.CalcHypotenuse(double.Parse(txtA.Text), double.Parse(txtB.Text));
    }

    public string CalcHypotenuse(double sideA, double sideB)
    {
        double hypotenuse = Math.Sqrt((sideA * sideA) + (sideB * sideB));
        string hypotenuseString = hypotenuse.ToString();
        return hypotenuseString;
    }

}

If you are only calling the method from within your form only, then make it private too so it can not be called from outside.