What does the To and Step mean in VBA? - vba

Question

Dim i As Long
Dim rows As Long
Dim rng3 As Range
rows = rng3.rows.Count
For i = rows To 1 Step (-1)
Does anyone know how this loop works? I'm confused on the meaning of rows To 1 Step (-1).

Answer 1

from high number To 1 adding (-1) each iteration
Note: It's adding because + AND - in mathematical logic evaluate to a -
If rows = 10 then
for i = 10 to 1 step -2 would mean loop back from 10 to 1 subtracting 2 from the i in each loop cycle.
adding a Debug.Print i inside the loop may give you a better clue.
Note: turn ON the Immediate Window hitting CTRL+G or View => Immediate Window from the VBE menu bar
An example loop increasing by 3 on each cycle.
for i = 1 to 10 step 3
debug.print i
next i
Usage
The step-back technique is mostly used when deleting rows from a spreadsheet.
To see the logic in practice see the following
How to select and delete every 3rd column
Delete entire excel column if all cells are zeroed
Excel VBA - Scan range and delete empty rows

Answer 2

When deleting rows, it is often common practise to start at the end and step backwards, this is so no rows are skipped.
Dim i As Long
Dim rows As Long
Dim rng3 As Range
rows = rng3.rows.Count
For i = rows To 1 Step (-1)
'delete row if "delete" is in column 1
If rng3.cells(i,1).Value = "delete" Then
rng3.Rows(i).EntireRow.Delete
End If
next i

Answer 3

Dim i as Integer
For i = 1 To 14 Step 3
Debug.Print i
Next i
In above code loop will iterate from 1 to 14 increment with 3 so output will be like
1 4 7 10 13
It means it can not cross 14 that is limit.
So whatever value is provided in step it will add into the variable use for looping purpose. Here
i = i +3
But in For loop in VBA, Step value can not be changed dynamically. For example:
Dim i As Integer
For i = 1 To 10 Step i
Debug.Print i
Next i
Here, before starting iteration Step is equal to the value of i that is the default value i.e. 0. So i will increment like below:
i = i+ i => i = i+0
So i will not increment here and loop will iterate for ever.
Now for below code:
Dim i as Integer
For i = 1 To 14 Step i+1
Debug.Print i
Next i
i will increment like :
i=i+(i+1) => i= i+(0+1) =>i = i+1
so it will increment by 1 and output will be 1 2 3 .... 14
Now for below code :
Dim i As Integer
i = 3
For i = 1 To 10 Step i
Debug.Print i
Next i
here, i is equal to 3 before loop execution, so Step value will be 3, but loop will start with i = 1 and will increment with 3 through out the loop.
here,
i = i+3
so output will be 1 4 7 10.
Now for some other variable:
Dim i As Integer
Dim j As Integer
j = 2
For i = 1 To 10 Step j
Debug.Print i
j = i
Next i
in above code Step value will be 2, so i will increment by 2 for every iteration whether j is modifying inside loop or not, it will not impact Step value, so output will be
1 3 5 7 9
Please correct me if I miss anything or something is wrong in this. Also suggest if there is any way for dynamic looping using For loop in VBA.