Q:

Excel macro - paste only non empty cells from one sheet to another

Below is the code which I am using to copy cells from one sheet and paste in to another. 
Sheets("codes").Select
Range("A5:A100").Select
Selection. Copy
Sheets("Sheet2").Select
Range("B28").Select
ActiveSheet. Paste

The problem with this is some cells in this range are blank but I do not want them to be copied to Sheet2.  I have got some idea from here but this method is too long.  Is there a way I can iterate on the selection and check if the value is non-empty and paste.  This way I can also paste some other text (eg #NA) in the blank cells. 

A:

Looks like you may be making some common rookie mistakes here (it's okay we all did it).  

VBA example with line-by-line explanations
TIP: Try not to use "Select" or "Copy".  Why use select when all you have to do is reference the cells themselves?  For example, instead of using
Sheets("codes").Select
Range("A5:A100").Select
Selection. Copy
Sheets("Sheet2").Select
Range("B28").Select
ActiveSheet. Paste

Just use
dim mySheet as Worksheet, myOtherSheet as Worksheet, myBook as Workbook 'Define your workbooks and worksheets as variables
set myBook = Excel. ActiveWorkbook
set mySheet = myBook. Sheets("codes")
set myOtherSheet = myBook. Sheets("Sheet2")

dim i as integer, j as integer 'Define a couple integer variables for counting

j = 28 'This variable will keep track of which row we're on in Sheet2 (I'm assuming you want to start on line 28)
for i = 5 to 100 'This is the beginning the the loop which will repeat from 5 to 100 . . . 
   if mySheet. Cells(i,1).value <> "" then ' . . .  for each digit, it will check if the cell's value is blank.  If it isn't then it will . . . 
      myOtherSheet. Cells(j,2).value = mySheet. Cells(i,1).value ' . . .  Copy that value into the cell on Sheet2 in the row specified by our "j" variable. 
      j = j + 1 'Then we add one to the "j" variable so the next time it copies, we will be on the next available row in Sheet2. 
   end if
next i 'This triggers the end of the loop and moves on to the next value of "i". 

I did the same thing all the time when I first started, and it never works out right. " Select" causes errors left and right.  Use my code, read the comments, and you'll be fine.  A quick WARNING: I don't have Excel on this computer so I couldn't test the code.  If it doesn't work for some reason, leave me a comment and tomorrow I'll fix it at work. 
The above code will omit blank cells completely when copying the data over to your second sheet.  If you want to input a certain text for blank cells instead (like "N/A"), then you can use the following:
 dim mySheet as Worksheet, myOtherSheet as Worksheet, myBook as Workbook 'Define your workbooks and worksheets as variables
 set myBook = Excel. ActiveWorkbook
 set mySheet = myBook. Sheets("codes")
 set myOtherSheet = myBook. Sheets("Sheet2")

 dim i as integer, j as integer 'Define a couple integer variables for counting

 j = 28 'This variable will keep track of which row we're on in Sheet2 (I'm assuming you want to start on line 28)
 for i = 5 to 100 'This is the beginning the the loop which will repeat from 5 to 100 . . . 
    if mySheet. Cells(i,1).value <> "" then ' . . .  for each digit, it will check if the cell's value is blank.  If it isn't then it will . . . 
       myOtherSheet. Cells(j,2).value = mySheet. Cells(i,1).value ' . . .  Copy that value into the cell on Sheet2 in the row specified by our "j" variable. 
    else 'If the cell is blank, then . . . 
       myOtherSheet. Cells(j,2).value = "N/A" ' . . .  place the text "N/A" into the cell in row "j" in Sheet2. 
    end if 'NOTICE we moved the "end if" statement up a line, so that it closes the "if" statement before the "j = j + 1" statement. _ 
      This is because now we want to add one to the "j" variable (i.e., move to the next available row in Sheet2) regardless of whether the cell in the "codes" sheet is blank or not. 
       j = j + 1 'Then we add one to the "j" variable so the next time it copies, we will be on the next available row in Sheet2. 
 next i 'This triggers the end of the loop and moves on to the next value of "i". 

A:

Easy:  
  Sheet1.Range("A1:a500").SpecialCells(xlCellTypeConstants).Copy Sheet2.Range("b2")

I used xlCellTypeConstants but there are many other possibilities. 
Sheet1 is generally equivalent to Sheets("Sheet1").  The first one is the name in the VBE (programmer view), the second is the name in the user interface (user view).  I generally prefer the fiirst syntax because it is shorter and allows renaming the sheets (for the user) without impacting the code.