Microsoft KB Archive/202781

= XL98: How to Get Prime Numbers or Factors =

Article ID: 202781

Article Last Modified on 10/11/2006

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APPLIES TO


 * Microsoft Excel 98 for Macintosh

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This article was previously published under Q202781





SUMMARY
A prime number is any integer that can be divided evenly only by itself and one. A factor of a number is an integer that can be evenly divided into that number. This article contains Microsoft Visual Basic for Applications macros for Excel that you can use to determine all the prime numbers within a range, or to derive all of the factors of a number.



MORE INFORMATION
Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. To create the macros, follow these steps:

 Save and close any open workbooks, and then create a new workbook. Start the Visual Basic Editor (press OPTION+F11), and on the Insert menu, click Module.  Type the following code in the module: Sub GetFactors Dim Count As Integer Dim NumToFactor As Single 'Integer limits to < 32768 Dim Factor As Single Dim y As Single Dim IntCheck As Single Count = 0 Do        NumToFactor = _ Application.InputBox(Prompt:="Type integer", Type:=1) 'Force entry of integers greater than 0. IntCheck = NumToFactor - Int(NumToFactor) If NumToFactor = 0 Then Exit Sub 'Cancel is 0 -- allow Cancel. ElseIf NumToFactor < 1 Then MsgBox "Please enter an integer greater than zero." ElseIf IntCheck > 0 Then MsgBox "Please enter an integer -- no decimals." End If        'Loop until entry of integer greater than 0. Loop While NumToFactor <= 0 Or IntCheck > 0 For y = 1 To NumToFactor 'Put message in status bar indicating the integer being checked. Application.StatusBar = "Checking " & y        Factor = NumToFactor Mod y         'Determine if the result of division with Mod is without _ remainder and therefore a "factor". If Factor = 0 Then 'Enter the factor into a column starting with the active cell. ActiveCell.Offset(Count, 0).Value = y           'Increase the amount to offset for next value. Count = Count + 1 End If     Next 'Restore Status Bar. Application.StatusBar = "Ready" End Sub Sub GetPrime Dim Count As Integer Dim BegNum As Single 'Integer limits to < 32768 Dim EndNum As Single Dim Prime As Single Dim flag As Integer Dim IntCheck As Single Count = 0 Do        BegNum = _ Application.InputBox(Prompt:="Type beginning number.", Type:=1) 'Force entry of integers greater than 0. IntCheck = BegNum - Int(BegNum) If BegNum = 0 Then Exit Sub 'Cancel is 0 -- allow Cancel. ElseIf BegNum < 1 Then MsgBox "Please enter an integer greater than zero." ElseIf IntCheck > 0 Then MsgBox "Please enter an integer -- no decimals." End If        'Loop until entry of integer greater than 0. Loop While BegNum <= 0 Or IntCheck > 0 Do        EndNum = _ Application.InputBox(Prompt:="Type ending number.", Type:=1) 'Force entry of integers greater than 0. IntCheck = EndNum - Int(EndNum) If EndNum = 0 Then Exit Sub 'Cancel is 0 -- allow Cancel. ElseIf EndNum < BegNum Then MsgBox "Please enter an integer larger than " & BegNum ElseIf EndNum < 1 Then MsgBox "Please enter an integer greater than zero." ElseIf IntCheck > 0 Then MsgBox "Please enter an integer -- no decimals." End If        'Loop until entry of integer greater than 0. Loop While EndNum < BegNum Or EndNum <= 0 Or IntCheck > 0 For y = BegNum To EndNum flag = 0 z = 1 Do Until flag = 1 Or z = y + 1 'Put message into Status Bar indicating the integer and _ divisor in each loop. Application.StatusBar = y & " / " & z           Prime = y Mod z            If Prime = 0 And z <> y And z <> 1 Then flag = 1 End If           z = z + 1 Loop If flag = 0 Then 'Enter the factor into a column starting with the active cell. ActiveCell.Offset(Count, 0).Value = y           'Increase the amount to offset for next value. Count = Count + 1 End If     Next y      'Restore Status Bar. Application.StatusBar = "Ready" End Sub  On the File menu, click Close and Return to Microsoft Excel. Switch to the worksheet on which you want to run the macro, and click a cell in which you want to create the column of factors or prime numbers. On the Tools menu, point to Macro, and then click Macros. Click GetFactors, and then click Run to get the factors.

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Click GetPrime, and then click Run to get the list of prime numbers.</li></ol>

NOTE: Although these macros can find prime numbers for a large range of numbers and factors for large numbers, running such code may take a very long time. For this reason, the status bar shows the progress while the macro runs.

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