export gridview to excel sheel in windows based app

Question

private void btnexport_Click(object sender, EventArgs e)

{

// creating Excel Application

Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();

// creating new WorkBook within Excel application

Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);

// creating new Excelsheet in workbook

Microsoft.Office.Interop.Excel._Worksheet worksheet = null;

// see the excel sheet behind the program

app.Visible = true;

// get the reference of first sheet. By default its name is Sheet1.

// store its reference to worksheet

worksheet = workbook.Sheets["Sheet1"];

worksheet = workbook.ActiveSheet;

// changing the name of active sheet

worksheet.Name = "Exported from gridview";

// storing header part in Excel

for (int i = 1; i < dataGridView1.Columns.Count + 1; i++)

{

worksheet.Cells[1, i] = dataGridView1.Columns[i - 1].HeaderText;

}

// storing Each row and column value to excel sheet

for (int i = 0; i < dataGridView1.Rows.Count - 1; i++)

{

for (int j = 0; j < dataGridView1.Columns.Count; j++)

{

worksheet.Cells[i + 2, j + 1] = dataGridView1.Rows[i].Cells[j].Value.ToString();

}

}

workbook.SaveAs("D:\\output.xls", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive, Type.Missing, Type.Missing, Type.Missing, Type.Missing);

app.Quit();

}

this is the code i had entered even though there is a error