Dynamically Insert Rows and Columns to GridView like Excel in ASP.Net

Here I have created sample that will help you out.

HTML

<div>
    <table border="0" cellpadding="0" cellspacing="0">
        <tr>
            <td>
                Enter Number of Rows Count:
            </td>
            <td>
                <asp:TextBox ID="txtRows" runat="server" />
            </td>
        </tr>
        <tr>
            <td>
                Enter Number of Columns Count:
            </td>
            <td>
                <asp:TextBox ID="txtColumns" runat="server" />
            </td>
        </tr>
        <tr>
            <td colspan="2" align="center">
                <asp:Button ID="btnCreate" Text="Create" runat="server" OnClick="Create" />
            </td>
        </tr>
    </table>
    <br />
    <br />
    <asp:GridView ID="gvData" runat="server" AutoGenerateColumns="true" />
</div>

Code

protected void Create(object sender, EventArgs e)
{
    this.gvData.DataSource = CreateData(Convert.ToInt32(txtRows.Text.Trim()), Convert.ToInt32(txtColumns.Text.Trim()));
    this.gvData.DataBind();
}

private DataTable CreateData(int rows, int columns)
{
    DataTable dt = new DataTable();
    for (int col = 0; col < columns; col++)
    {
        string letter = GetLetter(col + 1);
        dt.Columns.Add(letter);
    }
    for (int i = 0; i < rows; i++)
    {
        DataRow dr = dt.NewRow();
        for (int row = 0; row < columns; row++)
        {
            dr[row] = GetLetter(row + 1) + (dt.Rows.Count + 1);
        }
        dt.Rows.Add(dr);
    }
    return dt;
}

public string GetLetter(int column)
{
    string columnString = "";
    decimal columnNumber = column;
    while (columnNumber > 0)
    {
        decimal currentLetterNumber = (columnNumber - 1) % 26;
        char currentLetter = (char)(currentLetterNumber + 65);
        columnString = currentLetter + columnString;
        columnNumber = (columnNumber - (currentLetterNumber + 1)) / 26;
    }
    return columnString;
}

Screenshot