gui code to pass values from editbox to listbox and viceversa

i have three edit boxes "first","second" and "result" and a list box "listbox1". i need to pass the value from "result" to "list box1" and the final value from "listbox1" to "first". the "first" and "second" edit box values are added and the result is stored in "result" edit box. can anyone please provide me with the code.