Given Dropdown-Script in C# - compiling problems

I am referring to this script. I get a compiling error like "Expression denotes a `type', where a`variable', `value' or`method group' was expected" but cant see the problem. It works fine with JS though but that is no option in my case. Here is the code:

using UnityEngine;

using System.Collections;

public class gui : MonoBehaviour { public GameObject myGuiText;

private bool tabKeyPressed = false;
private bool tKeyPressed = false;

private bool showList = false;
private bool picked = false;

private int listEntry = 0;            

private GUIContent[] list = new GUIContent[5];
private GUIStyle listStyle = new GUIStyle();   

void Start()
{        
    // Make some content for the popup list
    //list = new GUIContent[5];
    list[0] = new GUIContent("Foo");
    list[1] = new GUIContent("Bar");
    list[2] = new GUIContent("Thing1");
    list[3] = new GUIContent("Thing2");
    list[4] = new GUIContent("Thing3");

    // Make a GUIStyle that has a solid white hover/onHover background to indicate highlighted items
    //listStyle = new GUIStyle();
    listStyle.normal.textColor = Color.white;
    Texture2D tex = new Texture2D(2, 2);
    listStyle.hover.background = tex;
    listStyle.onHover.background = tex;
    listStyle.padding.left = listStyle.padding.right = listStyle.padding.top = listStyle.padding.bottom = 4;

}

void OnGUI()
{
        Rect rect = new Rect(120, 150, 100, 20);                          
        if (Popup.List(rect, showList, listEntry, GUIContent("hello"), list, listStyle))
        {
            picked = true;
        }

The "Popup.cs" is placed in the StandardAssets folder under Scripts as it should be. Any suggestions?

The line in OnGUI():

if (Popup.List(rect, showList, listEntry, GUIContent("hello"), list, listStyle))

should probably be

if (Popup.List(rect, ref showList, ref listEntry, new GUIContent("hello"), list, listStyle))

Remember in C# you have to prefix variable creation with the word "new". Also, if you are passing in reference arguments, you have to prefix the variables you pass into the function with "ref".