input array is longer than the number of columns in my table

I have this code:

int flag = 0;
int num = 0;
int price, totprice, qty;
string product;

private void ProductsGV_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    product = ProductsGV.SelectedRows[0].Cells[1].Value.ToString();
    //qty =  Convert.ToInt32(OrderQtyTb.Text);
    price = Convert.ToInt32(ProductsGV.SelectedRows[0].Cells[3].Value.ToString());
    //totprice = qty * price;
    flag = 1;
}

private void button4_Click(object sender, EventArgs e)
{
    if (OrderQtyTb.Text == "")
        MessageBox.Show("Please Enter Quantity");
    else if (flag == 0)
        MessageBox.Show("Please Select Product");
    else
    {
        num = num + 1;
        qty = Convert.ToInt32(OrderQtyTb.Text);
        totprice = qty * price;
        DataTable table = new DataTable();
        table.Rows.Add(num, product, qty, price, totprice);
        OrdersGV.DataSource = table;
        flag = 0;
    }
}

I get an error on this line:

table.Rows.Add(num, product, qty, price, totprice);

> input array is longer than the number of columns in this table

The purpose of the code is to let me input a quantity. Then I will click on the product list table and after that I will now click the "Add to Order" button. I want the button to reveal the new quantity on the OrdersGV.

The problem is this line:

DataTable table = new DataTable();  

This makes a brand new table, with no columns defined at all, and the DataTable type requires you to use a well-defined schema.

You don't want to create a new DataTable here. You want to find the existing data source that is already showing in the grid, and add the row to that. If (and only if!) there is none, you need to create a DataTable object with defined Columns.

You don't need to new the DataTable. It should only be initial with the dataSource of OrdersGV:

 DataTable table = OrdersGV.DataSource as DataTable;
 table.Rows.Add(num, product, qty, price, totprice);