请问各位大侠，以下VB代码是什么意思

Question

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function ShowWindow Lib "user32" (ByVal hWnd As Long, ByVal nCmdShow As Long) As Long
Private Declare Function DrawMenuBar Lib "user32" (ByVal hWnd As Long) As Long
Private Declare Function SetFocus Lib "user32" (ByVal hWnd As Long) As Long
Private Const GWL_STYLE As Long = (-16)
Private Const GWL_EXSTYLE As Long = (-20)
Private Const WS_CAPTION As Long = &HC00000
Private Const WS_EX_DLGMODALFRAME As Long = &H1
Private Const SC_CLOSE As Long = &HF060
Private Const SW_SHOW As Long = 5

Answer 1

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
以这个函数为例，Private Declare Function是VB中引用WindowsAPI函数的固定格式，必须用Declare声明。FindWindow是需要用的API函数名，Lib "user32"是需要用到的库名。Alias "FindWindowA" 是说，这个函数（即FindWindow)还有一个别名，叫做FindWindowA，后面括号里的就是和普通函数一样的参数
ByVal lpClassName As String表示需要一个字符串作为窗口类的名子
ByVal lpWindowName As String表示需要一个字符串作为窗口的名子
下面的几个API函数同上，不再赘述
至于最后的常量声明，是为了方便使用的，比如窗口类的某一属性=SW_SHOW，其实你直接可以写，属性=5，但是为了直观且方便记忆，就使用sw_show代替5，不过VB中并没有定义sw_show=5，因此需要你自己定义一下，所以就有了Private Const SW_SHOW As Long = 5 这条语句。其他类似，希望你能明白。有问题再Hi我

Answer 2

声明 Window API

Answer 3

补充一下段程序的用意：
第一个函数查找出给定名字程序是否运行
第二个是查找到程序实例的句柄，可供操作
第三个是重新设置窗口的参数
第三个是重新显示窗口出。
第四个是设置窗口菜单
第五个是定义焦点。设置为可操作。

Answer 4

就是申明和定义一些常量