1. Computer Science 1000 Spreadsheets IV Permission to redistribute or use these slides is strictly prohibited without permission

2. Relative References as noted before, Excel seems to do the right thing when it fills when filling from cell D2, the formula =B2*C2 automatically became =B3*C3 when applied to cell D3 how did it know to do that?

3. Relative References when we make a reference using the syntax defined so far, Excel considers it a relative reference behind the scenes, a relative reference is not defined as a fixed location, but as a location relative to the current cell stated another way, the formula Excel uses in D2 is “the cell two columns behind me times the cell one column behind me”

4. Relative References hence, when a relative reference is copied to a new cell, the formula is changed to maintain the same spatial relationship in our example, when the formula from D2 is copied to D3, the references are replaced, so that the new references are “two columns behind D2” and “one column behind D2”

5. Relative References relative references work across rows and columns they even work across multiple sheets and multiple workbooks (coming soon!)

6. Relative References - Practice suppose that Canada decides to make driving gloves tax-exempt this means that we should compute GST on all items except driving gloves let’s reformat our receipt, so that the GST is computed for each individual item

7. Step 1: Reformat Table delete the appropriate rows from the table click on a row, right-click, and select Delete add the appropriate columns to the table

8. Step 2: Compute Tax for each Item two steps 1) determine the tax rate for that item Driving Gloves – 0% Everything else – 5% 2) multiply that tax rate to the item let’s do the first step first that is, let’s fill the Tax column with the appropriate tax rate can we do this, whilst keeping the formula consistent for each row? yes – use an if statement

9. The If Statement if the item is Driving Gloves tax rate is 0% otherwise tax rate is 5% Turn this into a True/False statement =IF( A2 = "Driving Gloves“, 0.00, 0.05 ) Boolean This is the value of the cell if the item is Driving Gloves This is the value of the cell if the item is not Driving Gloves True Value False Value

10. Notice that the appropriate choice was made for the tax rate (we’ll update this to the tax amount soon). Now, use the fill handle to fill the other columns with the same formula.

11. Because of relative referencing, the A2 reference in the first cell updates appropriately. Notice also that because of the if statement, the last cell has a 0% tax rate, as required.

12. Step 2: Compute Tax for each Item our example is coming, but it’s not quite the same as what was shown originally rather than showing the tax rate in that column, we should show the tax amount solution: multiply the tax rate by the price of the items

13. Now, fill the rest of the column with the new formula.

14. While the range is highlighted, format it to Currency.

16. Step 3: Compute Total for each Item the total for each item is computed as the price + tax using relative references, we need only compute the total for F2, and can fill the rest

17. Step 4: Compute the Bottom Totals the bottom totals are simply the sum of the prices in each cell note that since we have already computed that total in D7, we can simply fill the others with that formula

18. References suppose that Canada changes GST to 7% how many cells do we have to change in our previous example? all of the item rows (5 in our example) if this were a long receipt, would be cumbersome These formulas all have to be changed.

19. References instead of hard-coding 5% into our formula, let’s make it a cell reference we will store the current tax rate in cell H1

20. References now, replace the value 0.05 in our formula to refer to the tax rate cell

21. References conveniently, anytime we replace the tax rate, the tax in E2 updates appropriately

22. References what happens if we fill the other items to update their formula?

23. References remember: unless explicitly stated otherwise, a cell reference is relative in our formula for F2, referring to H1 meant “the cell one up and three to the right” hence, in the formula for F6, one up and three to the right = H5

24. Absolute References we can correct the previous example by using an absolute reference prepend the row/column name with $ by doing this, the cell reference is always the same for every filled cell

25. Absolute References notice that by using an absolute reference, we achieve our desired behaviour updating the tax rate changes all totals appropriately

26. Mixed Reference note that we have a mixed cell reference row is relative, while column is absolute or vice versa in this case, the relative reference will change during a fill, but the absolute reference won’t example: create a simple table that converts Canadian dollars to three other currencies, for a few specified amounts. furthermore, we only want to specify the formula once, and use fills for the rest

27. Mixed References For each cell, we want to multiply the left most value (amount) by the amount from its second row (rate). For the amount: - row should be relative - column should be absolute For the rate: - row should be absolute - column should be relative

28. Mixed References For the amount: - row should be relative - column should be absolute For the rate: - row should be absolute - column should be relative

29. Mixed References now, we can fill both rows and columns Notice that for the filled cells, the amount always refers to column A, while the rate always refers to row 2. However, the other references update appropriately.

30. Mixed References in our previous example, could we have used a mixed reference? yes – since our items are always in the same column, we could use a relative column reference