VB Nested Loop w/ Conditionals Syntax - excel

Question

I am new to VB and am having trouble getting a good grasp on the syntax of nested loops. For example:
For N = 8 To 22
For M = 4 To 19
If Cells(N, 3).Value >= 0 Then
Cells(M, 35).Value = 1
Else
Cells(M, 35).Value = 2
End If
Next M
Next N
I want this loop to check one column of cells and IF a cell contains a 0 or positive number it should return "1" in the other specified column. Otherwise, it should return a "2".
Unfortunately this loop currently is returning (ELSE) "2" in every cell of the new column. Any explanation of what I am doing wrong?

Answer 1

Nested loops like this operate by repeating the inner cycle from start to finish every time the outer cycle goes through one step. So for each N, every row M will have its cell in column 35 set to 1 or 2 (all the same) based on the value at row N and column 3. So in this case, the last row N must have a negative number or be missing, which sets every one of the output column cells to "2".
What I suspect you want is something more like this:
For N = 8 To 22
If Cells(N, 3) >= 0 Then
Cells(N - 4, 35) = 1
Else
Cells(N - 4, 35) = 2
End If
Next N
Note that there seems to be an off-by-one error in your original code as well, in that N goes over 15 rows, but M goes over 16 rows. Also, because .Value is the default property, you can leave it out.
Bonus: Generally speaking, you'll want something with fewer magic numbers, like this:
Option Explicit
Public Sub DoSomething()
Const ColTest As Integer = 3, ColResult As Integer = 35, DRowResult As Integer = -4
Const RowStart As Integer = 8, RowEnd As Integer = 22
Dim Row As Integer
For Row = RowStart To RowEnd
If Cells(Row, ColTest) >= 0 Then
Cells(Row + DRowResult, ColResult) = 1
Else
Cells(Row + DRowResult, ColResult) = 2
End If
Next Row
End Sub
Then, if you need to generalize it to work on different areas (by switching the constants to parameters), change where you've hardcoded it to work, or whatever else, it's simple to fix it at the top, once, and be sure you've got everything. It's also easier to understand in many cases. And, of course, Option Explicit is just good in general. (D in the constant names stands for delta/difference.)