Catégorie : Excel VBA Course

Creating a Sudoku Solver in Excel using VBA is a great way to practice algorithm design and automation. Here’s a detailed breakdown of how to build the solver in Excel VBA:

Overview:

The Sudoku puzzle consists of a 9×9 grid, where some cells are pre-filled with numbers, and others are empty (represented by zeroes or blanks). The solver will try to fill the empty cells by following these rules:

1. Each row must contain the numbers 1 to 9 without repetition.
2. Each column must contain the numbers 1 to 9 without repetition.
3. Each of the nine 3×3 sub-grids must contain the numbers 1 to 9 without repetition.

The VBA code will employ a backtracking algorithm to solve the puzzle, trying different numbers for empty cells and backtracking if it reaches an invalid state.

Steps to Implement the Solver in VBA:

1. Prepare the Worksheet

In your Excel worksheet, set up a 9×9 grid where the Sudoku puzzle will be displayed. You can represent the puzzle using a simple range like A1:I9, where each cell corresponds to a number in the puzzle.

2. Open the VBA Editor

Press Alt + F11 to open the Visual Basic for Applications (VBA) editor. In the editor, go to Insert → Module to create a new module where you will paste the VBA code.

3. Write the Sudoku Solver Code

Here’s the detailed VBA code for the Sudoku Solver using a backtracking algorithm:

Sub SolveSudoku()
    ' Define variables
    Dim sudoku(1 To 9, 1 To 9) As Integer
    Dim row As Integer, col As Integer
    Dim i As Integer, j As Integer   
    ' Read the Sudoku puzzle from the worksheet into the sudoku array
    For row = 1 To 9
        For col = 1 To 9
            sudoku(row, col) = Cells(row, col).Value
        Next col
    Next row   
    ' Call the recursive solver function
    If Solve(sudoku) Then
        ' Write the solved Sudoku puzzle back to the worksheet
        For row = 1 To 9
            For col = 1 To 9
                Cells(row, col).Value = sudoku(row, col)
            Next col
        Next row
        MsgBox "Sudoku Solved!"
    Else
        MsgBox "No solution exists."
    End If
End Sub

Function Solve(ByRef sudoku() As Integer) As Boolean
    ' This function attempts to solve the Sudoku using a backtracking algorithm
    Dim row As Integer, col As Integer
    Dim num As Integer   
    ' Find the next empty cell (0 represents an empty cell)
    If Not FindEmptyCell(sudoku, row, col) Then
        ' No empty cell found, puzzle is solved
        Solve = True
        Exit Function
    End If   
    ' Try all numbers from 1 to 9
    For num = 1 To 9
        ' Check if the number is valid for this cell
        If IsValid(sudoku, row, col, num) Then
            ' Assign the number to the cell
            sudoku(row, col) = num           
            ' Recursively attempt to solve the rest of the puzzle
            If Solve(sudoku) Then
                Solve = True
                Exit Function
            End If
            ' Backtrack if no solution was found
            sudoku(row, col) = 0
        End If
    Next num   
    ' No valid number was found, backtrack
    Solve = False
End Function

Function FindEmptyCell(ByRef sudoku() As Integer, ByRef row As Integer, ByRef col As Integer) As Boolean
    ' This function finds the next empty cell in the Sudoku puzzle (represented by 0)
    For row = 1 To 9
        For col = 1 To 9
            If sudoku(row, col) = 0 Then
                FindEmptyCell = True
                Exit Function
            End If
        Next col
    Next row
    FindEmptyCell = False
End Function

Function IsValid(ByRef sudoku() As Integer, row As Integer, col As Integer, num As Integer) As Boolean
    ' This function checks if a number is valid for a given cell (row, col) in the Sudoku puzzle   
    ' Check if the number already exists in the row
    Dim i As Integer
    For i = 1 To 9
        If sudoku(row, i) = num Then
            IsValid = False
            Exit Function
        End If
    Next i   
    ' Check if the number already exists in the column
    For i = 1 To 9
        If sudoku(i, col) = num Then
            IsValid = False
            Exit Function
        End If
    Next i   
    ' Check if the number already exists in the 3x3 subgrid
    Dim startRow As Integer, startCol As Integer
    startRow = Int((row - 1) / 3) * 3 + 1
    startCol = Int((col - 1) / 3) * 3 + 1
    For i = startRow To startRow + 2
        For j = startCol To startCol + 2
            If sudoku(i, j) = num Then
                IsValid = False
                Exit Function
            End If
        Next j
    Next i  
    ' The number is valid if it isn't in the row, column, or subgrid
    IsValid = True
End Function

Explanation of the Code:

1. Sub SolveSudoku: This is the main subroutine that reads the Sudoku puzzle from the Excel worksheet, calls the recursive Solve function, and then writes the solved puzzle back to the worksheet.
2. Function Solve: This is the recursive backtracking function that solves the Sudoku puzzle. It tries to fill the empty cells one by one by placing numbers 1-9 and checking if they are valid. If a number leads to an invalid state, it backtracks (removes the number and tries the next one).
3. Function FindEmptyCell: This function searches for the next empty cell (0) in the puzzle. It returns True if an empty cell is found, and False if the puzzle is completely filled.
4. Function IsValid: This function checks if placing a given number in a specific cell is valid. It checks the row, column, and 3×3 subgrid to ensure no duplicates.

5. Using the Solver:

• Enter your Sudoku puzzle in the range A1:I9 (9×9 grid). Use 0 or leave the cells empty for the puzzle’s blanks.
• Run the macro by pressing Alt + F8, selecting SolveSudoku, and clicking Run.
• The solver will fill in the grid and display a message box when the puzzle is solved or if no solution exists.

6. Handling Edge Cases:

• If the puzzle has no solution (e.g., due to an invalid initial configuration), the solver will display a message saying « No solution exists. »
• Ensure that the input puzzle follows the basic rules of Sudoku to avoid inconsistencies or invalid states.

Conclusion:

This code utilizes the backtracking algorithm, a common approach to solving constraint satisfaction problems like Sudoku. It systematically tries potential solutions, backtracking when it encounters an invalid state, until it finds a valid solution or concludes that no solution exists.

1. Set Up the Excel Sheet:

Before you start the VBA code, you should create a grid in Excel that represents the Sudoku board. You can do this by selecting a 9×9 range of cells (for example, A1:I9).

2. VBA Code to Generate a Sudoku Puzzle:

Option Explicit
Dim SudokuGrid(1 To 9, 1 To 9) As Integer
Dim SolvedGrid(1 To 9, 1 To 9) As Integer
Sub GenerateSudokuPuzzle()
    Dim i As Integer, j As Integer
    ' Initialize the Sudoku grid
    Call GenerateSolution
    ' Remove some numbers to create the puzzle
    Call RemoveNumbers
    ' Display the puzzle in the Excel grid
    Call DisplayPuzzle
End Sub

Sub GenerateSolution()
    ' Fill the grid with a valid Sudoku solution
    Call FillGrid(1, 1)
End Sub

Function FillGrid(Row As Integer, Col As Integer) As Boolean
    Dim num As Integer
    If Row > 9 Then
        FillGrid = True
        Exit Function
    End If
    If Col > 9 Then
        FillGrid = FillGrid(Row + 1, 1)
        Exit Function
    End If
    If SudokuGrid(Row, Col) > 0 Then
        FillGrid = FillGrid(Row, Col + 1)
        Exit Function
    End If
    For num = 1 To 9
        If IsSafeToPlace(Row, Col, num) Then
            SudokuGrid(Row, Col) = num
            If FillGrid(Row, Col + 1) Then
                FillGrid = True
                Exit Function
            End If
            SudokuGrid(Row, Col) = 0
        End If
    Next num
    FillGrid = False
End Function

Function IsSafeToPlace(Row As Integer, Col As Integer, num As Integer) As Boolean
    ' Check if the number can be placed in the specified position
    Dim i As Integer, j As Integer
    ' Check the row
    For i = 1 To 9
        If SudokuGrid(Row, i) = num Then
            IsSafeToPlace = False
            Exit Function
        End If
    Next i
    ' Check the column
    For i = 1 To 9
        If SudokuGrid(i, Col) = num Then
            IsSafeToPlace = False
            Exit Function
        End If
    Next i
    ' Check the 3x3 box
    Dim startRow As Integer, startCol As Integer
    startRow = (Row - 1) \ 3 * 3 + 1
    startCol = (Col - 1) \ 3 * 3 + 1
    For i = startRow To startRow + 2
        For j = startCol To startCol + 2
            If SudokuGrid(i, j) = num Then
                IsSafeToPlace = False
                Exit Function
            End If
        Next j
    Next i
    IsSafeToPlace = True
End Function

Sub RemoveNumbers()
    Dim removed As Integer
    removed = 0
    Dim i As Integer, j As Integer
    Dim index As Integer
    Dim numbers(81) As Integer
    For i = 1 To 81
        numbers(i) = i
    Next i
    ' Shuffle numbers array
    For i = 1 To 81
        index = Int((81 - 1 + 1) * Rnd + 1)
        Dim temp As Integer
        temp = numbers(i)
        numbers(i) = numbers(index)
        numbers(index) = temp
    Next i
    ' Remove numbers to create the puzzle
    For i = 1 To 81
        Dim row As Integer, col As Integer
        row = (numbers(i) - 1) \ 9 + 1
        col = (numbers(i) - 1) Mod 9 + 1
        If SudokuGrid(row, col) <> 0 Then
            SudokuGrid(row, col) = 0
            removed = removed + 1
        End If
        If removed >= 40 Then Exit For
    Next i
End Sub

Sub DisplayPuzzle()
    Dim row As Integer, col As Integer
    For row = 1 To 9
        For col = 1 To 9
            If SudokuGrid(row, col) > 0 Then
                Cells(row, col).Value = SudokuGrid(row, col)
            Else
                Cells(row, col).Value = ""
            End If
        Next col
    Next row
End Sub

Explanation of the Code:

1. Global Arrays (SudokuGrid, SolvedGrid):
   • SudokuGrid: This is the array that holds the current state of the puzzle. It will be filled with numbers from 1 to 9 for the solution, and some numbers will be removed to create the puzzle.
   • SolvedGrid: This array holds the full, completed Sudoku solution.
2. Main Subroutine (GenerateSudokuPuzzle):
   • This is the main subroutine that drives the generation of the Sudoku puzzle. It first calls GenerateSolution to create a valid solution, then it calls RemoveNumbers to remove some numbers from the grid to make it a puzzle, and finally, it displays the puzzle in the Excel worksheet using DisplayPuzzle.
3. Generating the Solution (GenerateSolution):
   • The GenerateSolution subroutine calls the FillGrid function, which is a recursive function that attempts to fill the grid with a valid solution.
4. Filling the Grid (FillGrid):
   • This function tries to fill the Sudoku grid row by row, column by column, and uses backtracking to find a valid configuration. If it encounters a situation where a number cannot be placed, it backtracks and tries another number.
5. Safety Check (IsSafeToPlace):
   • This function checks if placing a specific number in a given cell violates the Sudoku rules. It checks the current row, column, and the 3×3 subgrid to ensure the number doesn’t appear elsewhere.
6. Removing Numbers (RemoveNumbers):
   • After the grid has been filled with a valid solution, the RemoveNumbers subroutine randomly removes numbers from the grid to create the puzzle. It ensures that there are enough numbers removed (about 40 cells) to create a solvable puzzle.
7. Displaying the Puzzle (DisplayPuzzle):
   • This subroutine loops through the SudokuGrid and displays the numbers in the corresponding cells of the Excel sheet. If a cell contains a zero, it will display nothing.

How to Use the Code:

1. Open your Excel workbook and press ALT + F11 to open the VBA editor.
2. Insert a new module by clicking Insert > Module.
3. Paste the entire code into the module.
4. Close the VBA editor and return to your Excel workbook.
5. Run the GenerateSudokuPuzzle macro by pressing ALT + F8, selecting GenerateSudokuPuzzle, and clicking « Run ».

This code will generate a random Sudoku puzzle every time it’s run, with some cells filled and others left empty. You can adjust the number of cells to remove by changing the condition in RemoveNumbers (currently set to remove 40 cells).

Step 1: Understanding the Requirements

A stopwatch in Excel should:

• Start counting time when triggered.
• Pause and resume when needed.
• Reset to zero.
• Display the elapsed time dynamically.
• Work without freezing Excel (using Application.OnTime instead of DoEvents).

Step 2: Creating the User Interface (UI)

Before writing the VBA code, let’s create a simple UI in an Excel worksheet:

1. Insert Buttons (using Form Controls) and link them to the macro:
   • Start Button (e.g., named « btnStart »)
   • Pause Button (e.g., named « btnPause »)
   • Reset Button (e.g., named « btnReset »)
2. Designate a Cell for Display:
   • Select a cell (e.g., B2) to display the elapsed time.

Step 3: Writing the VBA Code

Now, let’s write the VBA code for the stopwatch.

1. Declare Variables

We need to track:

• The start time
• The elapsed time before pausing
• Whether the stopwatch is running

Option Explicit
Dim startTime As Double
Dim elapsedTime As Double
Dim isRunning As Boolean
Dim nextTick As Date

2. Start Stopwatch

This macro initializes the stopwatch and begins updating the display every second.

Sub StartStopwatch()
    If Not isRunning Then
        ' Capture the start time if not already running
        startTime = Timer - elapsedTime
        isRunning = True
        UpdateTime
    End If
End Sub

Explanation:

• If the stopwatch isn’t running, we capture the start time (Timer is the number of seconds since midnight).
• We subtract the previously recorded elapsedTime (to allow resuming).
• isRunning is set to True and we start updating the time.

3. Update Displayed Time

This subroutine keeps updating the elapsed time.

Sub UpdateTime()
    If isRunning Then
        elapsedTime = Timer - startTime
        Sheet1.Range("B2").Value = Format(elapsedTime, "0.00") & " sec"
        ' Schedule the next update
        nextTick = Now + TimeValue("00:00:01")
        Application.OnTime nextTick, "UpdateTime"
    End If
End Sub

Explanation:

• Calculates elapsed time dynamically.
• Updates the assigned cell (B2).
• Schedules itself to run again in 1 second using Application.OnTime.

4. Pause Stopwatch

This macro stops the timer temporarily.

Sub PauseStopwatch()
    If isRunning Then
        isRunning = False
        Application.OnTime nextTick, "UpdateTime", , False
    End If
End Sub

Explanation:

• Stops Application.OnTime, preventing further updates.
• Stores the elapsedTime so it can resume later.

5. Reset Stopwatch

This resets everything to zero.

Sub ResetStopwatch()
    isRunning = False
    elapsedTime = 0     Sheet1.Range("B2").Value = "0.00 sec"
    Application.OnTime nextTick, "UpdateTime", , False
End Sub

Explanation:

• Stops the stopwatch.
• Resets elapsedTime to zero.
• Clears the scheduled Application.OnTime events.

Step 4: Assign Macros to Buttons

1. Right-click each button.
2. Select « Assign Macro ».
3. Link them as follows:
   • « StartStopwatch » → Start Button
   • « PauseStopwatch » → Pause Button
   • « ResetStopwatch » → Reset Button

Step 5: Testing the Stopwatch

1. Click Start → The time should begin updating.
2. Click Pause → The time should stop but remain visible.
3. Click Start again → The stopwatch should resume from where it stopped.
4. Click Reset → The timer should reset to 0.

Final Notes

• Application.OnTime ensures Excel remains responsive.
• The format « 0.00 sec » makes the output readable.
• The logic supports pausing and resuming, unlike traditional DoEvents-based loops.

A Waterfall Chart is used to visually illustrate cumulative effects of sequential positive and negative values, often for financial data like revenue, expenses, and net profit. Since Excel 2016 introduced a built-in Waterfall Chart, we will use VBA to create a Waterfall Chart dynamically for earlier Excel versions as well.

1. Understanding the Waterfall Chart

A Waterfall Chart consists of:

• Starting Value: The first column (e.g., « Opening Balance »).
• Positive and Negative Changes: Columns representing increases (green) and decreases (red).
• Ending Value: The last column (e.g., « Closing Balance »).
• Bridges: The cumulative flow of values.

Since Excel does not provide built-in Waterfall Charts before Excel 2016, we will use Stacked Column Charts and format them manually.

2. Data Structure for the Waterfall Chart

We need a structured dataset:

• Base Column: Helps position floating bars.
• Increase Column: Positive values.
• Decrease Column: Negative values converted to positive.

3. VBA Code to Create the Waterfall Chart

This VBA macro:

• Reads data from an active worksheet.
• Processes data into the required format.
• Creates a stacked column chart.
• Applies colors for increases (green) and decreases (red).
• Removes the base series from visibility.

VBA Code

Sub CreateWaterfallChart()
    Dim ws As Worksheet
    Dim chartObj As ChartObject
    Dim chartWaterfall As Chart
    Dim lastRow As Long
    Dim rngCategory As Range, rngBase As Range, rngIncrease As Range, rngDecrease As Range
    ' Set the worksheet
    Set ws = ActiveSheet
    ' Find the last row of data
    lastRow = ws.Cells(ws.Rows.Count, 1).End(xlUp).Row
    ' Define data ranges
    Set rngCategory = ws.Range("A2:A" & lastRow) ' Categories
    Set rngBase = ws.Range("C2:C" & lastRow) ' Base values
    Set rngIncrease = ws.Range("D2:D" & lastRow) ' Increase
    Set rngDecrease = ws.Range("E2:E" & lastRow) ' Decrease
    ' Add a new chart
    Set chartObj = ws.ChartObjects.Add(Left:=300, Width:=500, Top:=50, Height:=350)
    Set chartWaterfall = chartObj.Chart
    ' Set chart type
    chartWaterfall.ChartType = xlColumnStacked
    ' Add series
    With chartWaterfall
        .SetSourceData Source:=Union(rngBase, rngIncrease, rngDecrease)
        ' Format Base Series (Make it invisible)
        With .SeriesCollection(1)
            .Format.Fill.Visible = msoFalse
            .Border.LineStyle = xlNone
        End With
         ' Format Increase Series (Green)
        With .SeriesCollection(2)
            .Format.Fill.ForeColor.RGB = RGB(0, 176, 80) ' Green
        End With
        ' Format Decrease Series (Red)
        With .SeriesCollection(3)
            .Format.Fill.ForeColor.RGB = RGB(192, 0, 0) ' Red
        End With     
        ' Set Axis Titles
        .Axes(xlCategory).HasTitle = True
        .Axes(xlCategory).AxisTitle.Text = "Categories"
        .Axes(xlValue).HasTitle = True
        .Axes(xlValue).AxisTitle.Text = "Values"     
        ' Chart title
        .HasTitle = True
        .ChartTitle.Text = "Waterfall Chart"
    End With
    ' Cleanup
    Set ws = Nothing
    Set chartObj = Nothing
    Set chartWaterfall = Nothing
    Set rngCategory = Nothing
    Set rngBase = Nothing
    Set rngIncrease = Nothing
    Set rngDecrease = Nothing
    MsgBox "Waterfall Chart Created Successfully!", vbInformation, "Success"
End Sub

4. Explanation of the VBA Code

• Data Selection:
  • The macro identifies the last row (lastRow) for dynamic range selection.
  • It assigns each column (Categories, Base, Increase, Decrease) to a VBA Range variable.
• Chart Creation:
  • Adds a new ChartObject to the active worksheet.
  • Defines it as a Stacked Column Chart (xlColumnStacked).
• Series Formatting:
  • Base Series (Series 1) is hidden to create the floating effect.
  • Increase Series (Series 2) is set to Green (RGB(0, 176, 80)).
  • Decrease Series (Series 3) is set to Red (RGB(192, 0, 0)).
• Axis and Titles:
  • Labels the X-axis as « Categories » and the Y-axis as « Values ».
  • Assigns the title « Waterfall Chart ».
• User Notification:
  • Displays a message box confirming chart creation.

5. How to Use the VBA Macro

• Open an Excel workbook and enter the data structure mentioned earlier.
• Press ALT + F11 to open the VBA Editor.
• Click Insert > Module and paste the VBA code.
• Run the macro by pressing F5 or from Developer > Macros > Run.

6. Conclusion

This VBA macro dynamically creates a Waterfall Chart in Excel, making it useful for users who don’t have Excel 2016 or later. It ensures:

• Automatic formatting with green/red color-coding.
• Dynamic data handling.
• User-friendly execution via a macro.

1. What is a UserForm?

A UserForm is a custom dialog box that allows users to interact with VBA applications in Excel. It provides a graphical interface to input and display data using controls like text boxes, labels, buttons, combo boxes, and list boxes.

2. Steps to Create a UserForm in Excel VBA

Step 1: Open the VBA Editor

1. Open Excel.
2. Press ALT + F11 to open the VBA Editor.
3. In the VBA Editor, go to Insert → UserForm.

A blank UserForm will appear along with the Toolbox, where you can add controls like text boxes, labels, buttons, etc.

Step 2: Add Controls to the UserForm

1. Drag and drop the following controls onto the UserForm:
   • Labels (for field names)
   • TextBoxes (for user input)
   • CommandButtons (for actions like Submit and Cancel)
   • ComboBox (for selection options)
   • ListBox (for multiple choices)
2. Rename each control appropriately using the Properties Window.

Step 3: VBA Code to Handle UserForm Events

Below is the complete VBA code for a UserForm that collects user details (Name, Age, and Gender) and stores them in an Excel sheet.

Code: UserForm with Data Entry Functionality

' Define the UserForm and its components
Option Explicit
Private Sub UserForm_Initialize()
    ' Initialize the ComboBox with gender options
    Me.cboGender.AddItem "Male"
    Me.cboGender.AddItem "Female"
    Me.cboGender.AddItem "Other"
End Sub

Private Sub cmdSubmit_Click()
    Dim ws As Worksheet
    Dim lastRow As Long
    ' Set the worksheet
    Set ws = ThisWorkbook.Sheets("UserData")
    ' Find the last empty row
    lastRow = ws.Cells(ws.Rows.Count, 1).End(xlUp).Row + 1
    ' Transfer data from the UserForm to the worksheet
    ws.Cells(lastRow, 1).Value = Me.txtName.Value
    ws.Cells(lastRow, 2).Value = Me.txtAge.Value
    ws.Cells(lastRow, 3).Value = Me.cboGender.Value
    ' Clear fields for new entry
    Me.txtName.Value = ""
    Me.txtAge.Value = ""
    Me.cboGender.Value = ""
    ' Inform user
    MsgBox "Data Submitted Successfully!", vbInformation, "Success"
End Sub

Private Sub cmdCancel_Click()
    ' Close the UserForm
    Unload Me
End Sub

4. Explanation of the Code

• UserForm_Initialize()

• This event is triggered when the form loads.
• It populates the ComboBox (cboGender) with gender options.

• cmdSubmit_Click()

• Retrieves values from TextBoxes and ComboBox.
• Finds the next available row in the worksheet.
• Saves the user’s input in the UserData worksheet.
• Clears the input fields for new entries.
• Displays a confirmation message.

• cmdCancel_Click()

Run ShowUserForm from the Macro window (ALT + F8) or assign it to a button.Closes the UserForm when the Cancel button is clicked.

5. How to Run the UserForm

• Ensure your Excel sheet has a worksheet named « UserData » with headers (Name, Age, Gender).
• Open the VBA Editor, go to Insert → Module, and add this macro:

1. 1. • Sub ShowUserForm()
      • Show
      • End Sub

6. Enhancements & Best Practices

• Input Validation: Add error handling to prevent empty fields.
• Database Storage: Store data in an external database (e.g., Access).
• UI Improvements: Use frames, colors, and formatting for better aesthetics.