主题：上个月代码该怎么写？

这样可靠一些：

Dim y As Integer = Date.Today.Year
Dim m As Integer = Date.Today.Month
Dim dt1 As New Date(y, m, 1)
dt1 = dt1.Addmonths(-1)
y = dt1.Year
m = Dt1.Month
Dim dt2 As New Date(y, m, Date.DaysInMonth(y, m))