How to update multiple rows using gridview in ASP.net on a SINGLE BUTTON CLICK?

place a textbox inside template field in fourth column

<asp:TemplateField HeaderText="Marks Scored">
    <ItemTemplate>
        <asp:TextBox runat="server" ID="txtMarksScored" />
    </ItemTemplate>
</asp:TemplateField>

Then inside button click event loop through grid view rows and get the textbox to get the value entered.

protected void Submit_Click(object sender, EventArgs e)
{
    foreach (GridViewRow gvr in GridView1.Rows)
    {
        TextBox txtMarksScored = (TextBox)gvr.FindControl("txtMarksScored");
        // Hope you understand what to do next?
        // txtMarksScored.Text
    }
}

A complete solution for multi line editing can be found at Matt Dotsons Blog. I use it in my own application.

What you need to do at minimum, besides registering the new gridview type and exchanging your existing asp:GridView with the new type, is to tell the GridView the ID of your "SaveButton". This button will then trigger the RowUpdating/Updated events for each row that changed.

Please refer to Dotsons Blog post for details and the downloadable sourcecode.

Although very late, but may be someone my look for it. Since you did not mentioned any condition or example of code, so I assume this, below is the code:

private void UpdateAllRecord()
    {
        StringBuilder query = new StringBuilder();
        for (int i = 0; i < GridViewName.Rows.Count; i++)
        {
            GridViewRow row = GridViewName.Rows[i];
            using (SqlConnection con = new SqlConnection(connStr)) //use your connection string
            {
                con.Open();
                SqlCommand cmd1 = new SqlCommand("update YourTable set  ColumnName=@ColumnName where Id= " + row.Cells[0].Controls.OfType<TextBox>().FirstOrDefault().Text + "  ", con);
                cmd1.Parameters.AddWithValue("@ColumnName", row.Cells[5].Controls.OfType<TextBox>().FirstOrDefault().Text);                
                cmd1.ExecuteNonQuery();
                con.Close();
            }
        }
    }

// Now call the UpdateAllRecord() to your button click event or any other event

protected void upload_Click(object sender, EventArgs e)
    {
        UpdateAllRecord()
    }