主题：关于日期计算问题

1、无法列出什么时候预期的。

2、看懂代码，再自由扩展，好么？

Dim dt_xyk As DataTable = DataTables("信用卡")
Dim dt_lsz As DataTable = DataTables("流水账")
Dim dt_dyyh As DataTable = DataTables("还款")
dt_dyyh.DataRows.Clear
Dim d As Date = new Date(Date.Today.Year, Date.Today.Month, 1)
Dim ds() As Date = {d, d.AddMonths(1)}
For Each d In ds
    For Each dr As DataRow In dt_xyk.DataRows
        Dim ndr As DataRow = dt_dyyh.AddNew
        ndr("账户名称") = dr("账户名称")
        ndr("账单日") = d.AddDays(dr("账单日")-1)
        ndr("转出") = dt_lsz.Compute("sum(金额)", "账户名称 = '" & ndr("账户名称") & "' and 日期 >= #" & ndr("账单日").addmonths(-1) & "# and 日期 <= #" & ndr("账单日") & "# and 类别 = '转出'")
        ndr("转入") = dt_lsz.Compute("sum(金额)", "账户名称 = '" & ndr("账户名称") & "' and 日期 >= #" & ndr("账单日").addmonths(-1) & "# and 日期 >= #" & ndr("账单日") & "# and 类别 = '转入'")
        Dim yq_out = dt_lsz.Compute("sum(金额)", "账户名称 = '" & ndr("账户名称") & "' and 日期 < #" & ndr("账单日").addmonths(-1) & "# and 类别 = '转出'")
        Dim yq_in = dt_lsz.Compute("sum(金额)", "账户名称 = '" & ndr("账户名称") & "' and 日期 < #" & ndr("账单日").addmonths(-1) & "# and 类别 = '转入'")
        ndr("信用额度") = dr("信用额度")
        ndr("当月应还") = ndr("转出") - ndr("转入") + yq_out + yq_in
        ndr("可用额度") = ndr("信用额度") - ndr("当月应还")
        If val(dr("还款日")) < val(dr("账单日")) Then
            ndr("还款日") = d.AddDays(dr("还款日")-1).AddMonths(1)
        Else
            ndr("还款日") = d.AddDays(dr("还款日")-1)
        End If
        If ndr("当月应还") > 0 Then
            If ndr("账单日") > Date.Today Then
                ndr("账单状态") = "未出账,没还款"
            Else
                ndr("账单状态") = "已出账,没还款"
            End If
        Else
            If ndr("账单日") > Date.Today Then
                ndr("账单状态") = "未出账,没还款"
            Else
                ndr("账单状态") = "已出账,已还款"
            End If
        End If
        ndr("账单月份") = Format(d, "yyyyMM")
    Next
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