VB.NET中FALSE与0值的问题

' 本程序为学习而写 , 没有任何实际意义 VB.NET

Public Class Point

        Private x As Single    'X Coordinate

        Private y As Single    'Y Coordinate

         ..........................

End Class

 

Public Class Line

Inherits Point

Private vertexA As Point

        Private vertexB As Point

 

Public Function SlopeOfLine() As Object

 

            Dim slope As Single

 

            If vertexA.propertyX = vertexB.propertyX Then

                slope = False   'false stands for that this line' slope dosn't exist.

            Else

                slope = (vertexA.propertyY - vertexB.propertyY) / _

                (vertexA.propertyX - vertexB.propertyX)

            End If

 

             Return slope

 

     End Function

    

     Public Function Parallel(ByVal l1 As Line) As Boolean

          

            If Me .SlopeOfLine() = l1.SlopeOfLine() Then

                Return True

            Else

                Return False

            End If

 

        End Function

 

         Public Function Vertical(ByVal l1 As Line) As Boolean

 

            If Me .Parallel(l1) Then       ' parallel is true, is not vertical

 

                Return False

 

                'when not parallel

            Else

                If (Me .SlopeOfLine() = 0 And l1.SlopeOfLine() = False ) Or _

                 (Me .SlopeOfLine() = False And l1.SlopeOfLine() = 0) Then

                    Return True

                ElseIf (Me .SlopeOfLine() * l1.SlopeOfLine() = -1) Then

                    Return True

                 End If

            End If

 

        End Function

 

    End Class

 

求斜率的函数 ( Function SlopeOfLine() As Object ) 因为在存在一个特殊情况 , 就是直线垂直于 X 轴时 , 其斜率是不存在的 , 而在其他情况下 , 直线的斜率为一浮点型数 , 所以这个函数存在两种类型的返回值 , 于是我就把其定义为 Object 类型 , 目的就是为了处理特殊情况 .

   然而在 Function SlopeOfLine() As Object 中 , 却 Dim slope As Single , 接下来 , 把特殊情况下的 slope 赋值为 FALSE, 而 FALSE 为 VB.NET 中的一关键字 , 是有特殊意义的 , 其值为 0.

   这样 , 在 Function Parallel(ByVal l1 As Line) As Boolean 中 , 会把一条斜率为 0 的直线和一条没有斜率的直线认为是平行的 , 这样 , 就产生了逻辑错误

 

   具体的改正方法是 , 把 slope 定义为 Object 型 , 并且在直线的斜率存在时 , 给其赋非关键字的值 .

 

Public Function SlopeOfLine() As Object

 

            Dim slope As Object

 

            If vertexA.propertyX = vertexB.propertyX Then

                slope = noSlope   ' noSlope stands for that this line' slope dosn't exist.

            Else

                slope = (vertexA.propertyY - vertexB.propertyY) / _

                (vertexA.propertyX - vertexB.propertyX)

            End If

 

             Return slope

 

     End Function

 

这样 , 就不会产生原程序中的逻辑错误了 .

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  2008年4月9日