func main() {
    var id int
    var ids []int
    var count int

    f, err := os.Create("xyz.txt")
    check(err)

    defer f.Close()

    for j := 0; j < 5; j++ {
        count = rand.Intn(100)
        for i := 0; i < product_count; i++ {
            id = rand.Intn(1000)
            ids = append(product_ids, product_id)
        }
        n2, err := f.Write(ids)
        check(err)
        fmt.Printf("wrote %d bytesn", n2)
    }
}