以下代码是打印汇总表中选择行的交易金额，为什么我选择了20行，以下代码只显示了10行，是什么原因？

Dim tbm As DataTable = DataTables("明细表")
Dim tbz As Table = Tables("汇总表")
Dim doc As New PrintDoc
Dim ra As New prt.RenderArea
Dim Date1 As Date =# 05-01-2012 #
Dim Date2 As Date = # 11-30-2012 #
For  n As Integer = tbz.TopPosition To tbz.BottomPosition
    Dim rt As New prt.RenderText
    Dim filter = "交易户名= \'" & tbz(n)("交易户名") & "\' And 交易日期 >= # 2012-05-01 # And 交易日期 <= # 2012-11-30 # "
    rt.text =format(date1,"D") & "至" & format(Date2,"D") & "交易金额" & tbm.Compute("sum(借方金额)",filter) & "元。"
    ra.Children.Add(rt) \'将打印对象添加到容器中
    n = n + 1
Next
doc.body.Children.Add(ra)
doc.Preview()

这句代码去掉 n = n + 1

n在for循环里面，就是自动加1的。