COMP 4—Power Tools for the Mind 1 Power Tools Spreadsheets What we’ll cover for this lecture topic: –The paper worksheet... –What are electronic spreadsheets? –Cells cell references cell contents –Formulas and functions –What are spreadsheets good for? –Relative and absolute cell referencing (critical!) Demos interspersed as time permits

The electronic spreadsheet The paper worksheet Worksheets were used in many businesses for inventory management and accounting. Key feature: columns to separate different types of information (‘fields’). Because columns sizes varied depending on the use, many formats were available. Accounting Ledgers (Items, debits, credits, tax info…) Inventory (Items, #in stock, supplier, wholesale $, retail $...) Payroll (Name, SSN, job title, mailing address, salary…) BOTTOM LINE BOTTOM LINE : Lots of paperwork and calculation! 2 Mid 70’s: Dan Bricklin & Bob Frankston--the story.

COMP 4—Power Tools for the Mind 3 Power Tools Each entry occupies a cell... It can hold: –numeric values –alphanumeric text (character strings). As labels; what about as data? –an entire formula. The real power! The electronic spreadsheet “The most brilliant software invention of the microcomputer era … “ Neill Graham Basically, it’s just a 2-dimensional table:

COMP 4—Power Tools for the Mind 4 Power Tools Remember Charles Babbage? Manual spreadsheets had lots of problems… –time-consuming to produce –difficult to edit and update –miscalculation errors –transcription errors (recording wrong number) With electronic spreadsheets… –calculations are automated (fast, reliable, & simple to modify!) –formatting can also be easily changed

COMP 4—Power Tools for the Mind 5 Power Tools Referencing a Cell In most electronic spreadsheets, columns are indexed by letters, and rows are indexed by numbers. A cell is identified and referenced by writing its column letter(s) followed by its row number. E.g., cell D3 is highlighted in the above picture. ABCDE

COMP 4—Power Tools for the Mind 6 Power Tools To refer to a block of contiguous cells, specify a starting cell and ending cell separated by a colon. E.g., the marked region below is C2:E4. Non-contiguous blocks of cells can be referenced using a list in which the references are separated by commas, e.g., the reference C2:E4,A1:A3 is the marked block above along with cells A1, A2 & A3. ABCDE Referencing a group of Cells

COMP 4—Power Tools for the Mind 7 Power Tools So what’s it good for? –Personal/professional budgets and budget scenarios –Building space allocation –Grades –Income statements, balance sheets –Investment analyses –Keeping track of nearly anything... all cell functions that use that cell’s value are automatically recalculated. Immensely USEFUL! When a cell value CHANGES….

COMP 4—Power Tools for the Mind 8 Power Tools Great for “what-if” analyses: –What if…. we decrease costs of good sold by 5%, what will our net earnings be? I earn an 80% on Exam 2, what will my average be? If my pay gets raised 5%, how much extra take- home pay will I get? Can I afford another loan? Demo 1 & 2….. Meet Microsoft Excel

COMP 4—Power Tools for the Mind 9 Power Tools Excel uses a very simple programming language: More about formulas cell references (names) Digression…really interested in? cell contents Nouns? Basic Verb Set (2-operand operations) includes: Arithmetic operators: + – * / ^ Comparison operators: = >= Boolean operators: And Or Not Functions!  Special symbols: $, : ( ) and:

COMP 4—Power Tools for the Mind 10 Power Tools Functions Many more operations available as functions. Functions take a collection of cell references as input, e.g.., SUM(A1:A5,B7,C8:C10) calculates the sum of the values cells A1:A5, B7, and C8:C10. A few particularly useful functions: – SUM: computes sum of all values – PRODUCT: computes product of all values – MAX: finds maximum value – MIN: finds minimum value

COMP 4—Power Tools for the Mind 11 Power Tools Fairly simple syntax for formulas. –AVERAGE: finds average value – COUNT: finds number of non-empty cells in the group that contain numerical data. – COUNTA: finds number of non-empty cells in group. – IF(condition,A,B): conditional formula. If condition is true, use formula A. Otherwise, use formula B. Mathematical precedence rules apply (use parentheses)

COMP 4—Power Tools for the Mind 12 Power Tools Formulas can depend upon other cells (which themselves might be the result of other formulas...). Powerful! = SUM(D4 : D12) = AVERAGE(A2:A200) Each is like a little computer program that lives in a cell.  Notice the colon:

Relative cell references How does Excel look at a cell reference in a formula? Excel interprets the formula in cell B4 this way: = (B1 + B2) * B3 Entry bar: B4 A B C = (B1 + B2) * B3 [Enter] Relative to where formula resides! Find value stored 3 rows up from formula cell, Add that to value stored 2 rows up from formula cell, Multiply that to value stored 1 row up from formula cell, Display answer. Note: formulas displayed. 13

SO WHAT? Why should you care? Because: What if I copy A4 to C5? What will C5 look like? A B C D = A1 + B You will want to RE-USE formulas you create as OFTEN as possible! ( Copy and Fill ) --You must know HOW Excel will INTERPRET your request! Row & cell references will change ! 14 = C + D2 3

What about here? Very same idea What if I copy C4 to A6? What will A6 look like? A B C D = C1 +C2 +C3 15 =A +A +A 3 4 5

What about here? What if I copy C4 to C5 ? What will C5 look like? A B C D = C1 +C2 +C3 Did we move columns? 16 =C +C +C But we DID move ROWS! 2 3 4

COMP 4—Power Tools for the Mind 17 Power Tools Important Tricks of the Trade When you COPY a formula from one cell to another, any RELATIVE references will follow: –That is: CELL REFERENCES will CHANGE in the target cell, as just seen. Placing the special symbol $ in front of the row or column identifier in a reference prevents Excel from changing that part of the reference when copying. ABSOLUTE

1 st : Excel interprets the formula this way: A B C D = $A$1 - B2 + C Find value stored in exactly CELL A1, Subtract from that: value stored in cell: 2 rows up and 1 col to the right; Add that to value in cell 1 row up and 2 cols to the right. Display answer. 18 What if I copy A4 to B5 ? What will B5 look like? =$A -C +D $1 3 4

COMP 4—Power Tools for the Mind 19 Power Tools Cell references are classified according to the absence or presence of the $ symbol. All three types are used depending on the problem (we’ll look at real examples later that show WHEN/WHY to use different references!) – Relative reference: Neither the row nor column identifier is preceded by $. E.g., B4. (the default) – Mixed reference: Either the row or column identifier is preceded by $, but not both. E.g., $B4 and B$4. –Absolute reference: Both the row and column identifiers are preceded by $. E.g., $B$4. Referencing cells in formulas

COMP 4—Power Tools for the Mind 20 Power Tools Important Tricks of the Trade, con’t When you move a formula, Excel automatically updates the cell references contained in formulas. –Examples coming… Nifty Feature: When you edit a formula, Excel will put color-coded boxes around the different cell references. Works great when trying to figure out what is wrong with a formula. DEMO 3