求解释解决办法

求解释
我在编写一个计算器的时候为什么必须这样写
  dim x as integer 
  dim y as integer 
  dim s as integer
  Private Sub btnjia_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnjia.Click
  x= val(text1.text)
  y = val (text2. text)
  s=x+y
  text3.text=s
  end sub
为什么写成这样就出错啊
  dim x as integer = val(text1.text)
  dim y as integer = val(text2.text)
  dim s as integer
  Private Sub btnjia_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnjia.Click
  s=x+y
  text3.text = s
  end sub
还有怎样让text3显示的为text1.text+text2.text=text3.text

[解决办法]
dim x as integer = val(text1.text)
你这样，text1还没有输入内容你就开始使用Text了
[解决办法]

VB.NET code

  Private Sub btnjia_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnjia.Click  '下面这三行变量定义要是搬到方法体里面就不会错了，也就是说在方法体外面的时候属于模块变量，  '组件 text1, text2 的 TEXT 属性都还没有被赋值；你后面再输入的值不会改变 x 和 y 最初所  '得到的值;  dim x as integer = val(text1.text)  dim y as integer = val(text2.text)  dim s as integer  s=x+y  text3.text = send sub