Percent of change calculation VB.NET

Posted on 2010-11-12
Last Modified: 2012-05-10
Attached is a screenshot of what should seemingly be a simple piece of code. I am attempting to calculate percent of change and avoid a divide by zero.....My code to get around the zero works, however i am getting the wrong answers with what i thought to be the base calculation
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub
    Private Function CalcPercent(ByVal NewVal As Integer, ByVal OldVal As Integer) As Decimal

        If NewVal = 0 And OldVal > 0 Then
            CalcPercent = -100
            Exit Function
        End If

        If NewVal > 0 And OldVal = 0 Then
            CalcPercent = 100
            Exit Function
        End If

        If NewVal = 0 And OldVal = 0 Then
            CalcPercent = 0
            Exit Function
        End If

        CalcPercent = (NewVal - OldVal) / OldVal * 100

    End Function
    Private Sub TestCalc()
        Dim myConnection As SqlConnection
        Dim myCommand As SqlCommand
        Dim myReader As SqlDataReader
        Dim prm As SqlParameter
        Dim NEWVALUE As Integer
        Dim OLDVALUE As Integer
        Dim EXPECTED As String
            myConnection = New SqlConnection(ConfigurationSettings.AppSettings("connectionString"))
            myCommand = New SqlCommand("TestPercentCalcsRTN", myConnection)
            myCommand.CommandType = CommandType.StoredProcedure

            myReader = myCommand.ExecuteReader()

            While myReader.Read
                OLDVALUE = myReader("OLDVALUE")
                NEWVALUE = myReader("NEWVALUE")
                EXPECTED = myReader("EXPECTED")
                Response.Write("OLDVALUE : " + Right("_____________" + Str(OLDVALUE), 10) + "   ")
                Response.Write("NEWVALUE : " + Right("_____________" + Str(NEWVALUE), 10) + "   ")
                Response.Write("CALCULATED : " + Right("_____________" + Str(CalcPercent(NEWVALUE, OLDVALUE)), 10))
                Response.Write("____EXPECTED : " + Right("_____________" + EXPECTED, 10) + "   " + "  <BR> ")
            End While

        Catch ex As Exception


            If Not myReader Is Nothing Then
                myReader = Nothing
            End If

            If Not myConnection Is Nothing Then
            End If

        End Try
    End Sub

Open in new window

Question by:shelbyinfotech
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 6
  • 2
LVL 37

Expert Comment

ID: 34123126
You just want
CalcPercent = NewVal/OldVal * 100
LVL 37

Expert Comment

ID: 34123132
Actually, I think you are a little confused. You are getting the percentage increase currently. Going from 50 to 100 is a 100% increase.
LVL 37

Expert Comment

ID: 34123174
Your data is correct, your expectations are wrong.
You don't need
        If NewVal = 0 And OldVal > 0 Then
            CalcPercent = -100
            Exit Function
        End If

It will do that automatically.

        If NewVal > 0 And OldVal = 0 Then
            CalcPercent = 100
            Exit Function
        End If

This shouldn't be 100, it should be infinite. Maybe you should use 99999 or something to make the ouput more indicative of the actual result.
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

LVL 37

Expert Comment

ID: 34123183
So ignore my first post. That will give you what the new value is as a percent of the old value.  Your original formula gives you the percentage change.

Author Comment

ID: 34123269
Case 1 is not giving me -5%
LVL 37

Expert Comment

ID: 34123328
Case 1 should not give you 5% If you want from 100% to 95%, that would be a 5% decrease.

When you go from 105% to 100% you are dropping 5 of the 105 so 5/105 is the correct drop amount. Converted to a percent gives 4.76% and some change, just like it is showing.
LVL 37

Accepted Solution

TommySzalapski earned 500 total points
ID: 34123387
You do have a formatting issue though.
Try this
CalcPercent = Round((NewVal - OldVal) / OldVal * 100,2)

Author Closing Comment

ID: 34123795

Featured Post

Salesforce Made Easy to Use

On-screen guidance at the moment of need enables you & your employees to focus on the core, you can now boost your adoption rates swiftly and simply with one easy tool.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Article by: jpaulino
XML Literals are a great way to handle XML files and the community doesn’t use it as much as it should.  An XML Literal is like a String ( Literal, only instead of starting and ending with w…
Calculating holidays and working days is a function that is often needed yet it is not one found within the Framework. This article presents one approach to building a working-day calculator for use in .NET.
Exchange organizations may use the Journaling Agent of the Transport Service to archive messages going through Exchange. However, if the Transport Service is integrated with some email content management application (such as an antispam), the admini…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

751 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question