Compare two sheets and find differences, copy to third sheet - vba

Question

I have been trying to compare two sheets. The sheets are versions, one made in August, the other in September. In Sheet1, column C I have a unique ID that could also be in sheet 2, but could also be not present. On the other hand, I could have NEW ID's in sheet 2, that are not present in Sheet1.
I am trying to:
Identify IDs not in "other" sheet, copy entire row to sheet3
Check if C-column value exists in other sheet, then it has to find
the differences in THOSE two rows, 12 columns out
Example, in sheet1:
ID Jan Feb Mar Apr May
14578596 125 125 125 0 10
22345697 10 10 10 10 20
12563654 150 150 75 75 75
85745896 890 890 890 890 790
and in sheet 2:
ID Jan Feb Mar Apr May
14578596 125 125 125 0 10
12563654 150 150 75 75 75
85745896 890 890 790 890 790
87544545 0 0 0 0 10
In sheet 3, it should copy over the newly added ID 87544545 and all the values in the following columns. It should copy over the ID's 22345697 entire row as well, as being non-existing in the other sheet is considered a difference.
For the others, that exist in both sheets, it should Take "Jan-Jan" and return the difference value. So it should lookup if "ID" exists in other sheet, if it does, compare the Jan-Feb-Mar with each other. Note that ID's are NOT in the same position in the sheets. With ID 85745896 it would return:
ID Jan Feb Mar Apr May
85745896 0 0 100 0 0
I have tried to look at topics such as
Compare data from 2 sheets and find mismatches
and
Check if two rows are the EXACT SAME in MS Excel but can't seem to make them work for my challenge here.

Answer 1

Sub compare()
For i = 1 To last_cell_mainSheet
For j = 1 To last_cell_sheet2
If Worksheets("main_sheet").Range("a" & i).Value = Worksheets("sheet2").Range("a" & j).Value
Then
Worksheets("main_sheet").Range("C" & i).Value = Worksheets("sheet2").Range("b" & j).Value
End If
Next j
Next i
End Sub

Answer 2

The easiest way to solve this is with excel formulas. (if you only want to do it once, or occasionally.) If you need to repeat if often (or have massive amounts of data) use VBA>
You will need to find out about VLOOKUP and IF and ISNA.
Essentially you can add a column to both sheets that looks up the ID in the other sheet and returns Y or N if it is found or not.
You formaula will be something like:
=IF(ISNA(VLOOKUP(MyIDCell,TheTableInTheOtherSheet, 1, false)),"N","Y")
TheTableInTheOtherSheet is a range starting with the ID column (and only neededing one column)
Do the Jan-Jan bit.
Again use a vlookup formula column on sheet1 to get the value of Jan from sheet2. The add a formula to compare them.
You formula will be something like:
=VLOOKUP(MyIDCell,TheTableInTheOtherSheet, 2, false)
TheTableInTheOtherSheet is a range starting with the ID column (and two columns wide)
2 get the second column value
Once you have the data you can sort or filter to reduce the list ot thsoe you need to copy to sheet 3 (best to sort). Then copy and paste them.