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Public Class Form1
    Private Sub btnDFT_Click(sender As Object, e As EventArgs) Handles btnDFT.Click
        ' Input data array
        Dim data() As Double = {1, 2, 3, 4, 5}
        ' Output array for DFT results
        Dim dft() As Complex
        ' Perform DFT
        dft = DFT(data)
        ' Display results
        For i As Integer = 0 To dft.Length - 1
            Console.WriteLine("DFT[" & i & "]: " & dft(i))
        Next
    End Sub

    ' Function to perform DFT on input array
    Public Function DFT(data() As Double) As Complex()
        Dim N As Integer = data.Length
        Dim dft(N - 1) As Complex
        For k As Integer = 0 To N - 1
            For n As Integer = 0 To N - 1
                dft(k) += New Complex(data(n) * Math.Cos(2 * Math.PI * k * n / N), -data(n) * Math.Sin(2 * Math.PI * k * n / N))
            Next
        Next
        Return dft
    End Function
End Class

To create a chart of COVID-19 cases in Kostroma Oblast, Russia in Excel, you can follow these steps:

    Obtain data on COVID-19 cases in Kostroma Oblast. This data should include the number of cases for each day or each week, and should be in a tabular format, such as a spreadsheet.

    Open Microsoft Excel and create a new workbook or open an existing one.

    Enter the data you obtained in step 1 into the spreadsheet. Make sure to include the dates or weeks as the first column and the number of cases as the second column.

    Select the data in the spreadsheet.

    Click on the "Insert" tab and select "Chart" from the ribbon.

    Choose the type of chart you want to create, such as a line chart or a bar chart.

    Customize the chart as desired, such as adding a title, axis labels, and a legend.

    Once the chart is created, you can move or resize it as desired.

    Finally, save the workbook.

Note that this is a general guide, it may be slight variations depending on the version of Excel you're using.