visualstudio请问这里为什么要有k ，k+1的作用是什么呢

Dim m, i, k As Integer
Dim Flag As Boolean
For m = 3 To 100
Flag =True
For i = 2 To Math. Sqrt(m)
If（m Mod i)）= O Then Flag=False
Next i
If Flag Then
k = k + 1
Labell. Text = Labell. Text &m&""
End If
Next m