Writing And Calling functions with in a form

Question

Hi,

    I am switching from VB to C# and facing a Problem for writing and calling function with in a form.

below is my code:

two textboxes which accepts value to be added and result in third textbox on button click event.

  public int Add(int i, int j)

        {

            int result = i + j;

            return result;

            

        }

     

        protected void btnResult_Click(object sender, EventArgs e)

        {

            int result = Add(tb1.Text, tb2.Text);

            tb3.Text =(result);

        }

But showing error invalid argument...

Plz help...