How to Get Prime Numbers or Factors (202782)

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:

1. Save and close any open workbooks, and then create a new workbook.
2. Create a new module:
   
   In Microsoft Excel 97, start the Visual Basic Editor by pressing ALT+F11.
   
   In Microsoft Excel 5.0, or 7.0, click Macro and Module on the Insert menu.
3. 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 thus 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
   					

4. 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.
5. On the Tools menu, point to Macro, and then click Macros.
6. Click GetFactors, and then click Run to get the factors.
   
   -or-
   
   Click GetPrime, and then click Run to get the list of prime numbers.

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.