Private Sub Form_Click()
  Dim a, b, c, p, s As Integer
      Do
          a = InputBox("请输入边长,输入-1退出程序", "计算三角形面积")
          b = InputBox("请输入边长,输入-1退出程序", "计算三角形面积")
          c = InputBox("请输入边长,输入-1退出程序", "计算三角形面积")
      If a < 0 Or b < 0 Or c < 0 Then Exit Do
      If a + b < c Or b + c < a Or c + a < b Then
              Print "不能构成三角形"
      Else
              p = (a + b + c) / 2
              s = Sqr(p * (p - a) * (p - b) * (p - c))
              Print "该三角形面积为：", s
      End If
    Loop While a > 0
Print "退出"
End Sub

无论输入多少的边长，就是不执行Else下面的语句块

应该是 Dim a, b, c, p, s As Integer  这句的问题，应该要用  dim a as integer,b as integer.......这样
If a + b < c Or b + c < a Or c + a < b Then   这句也有问题，应该把“<”换成“<=”
刚学，见笑了