1. CSC 110 - Intro. to Computing Lecture 11: Spreadsheets

2. Announcements Make sure you get a “PALGO” handout  Will use handout for next few weeks Service learning pages due today  For future deadlines, please e-mail me pages Homework #3 handed out at end of class  Due in my box at 5PM Monday, Feb. 27 th  Quiz #3 will be in class next Thursday

3. Computer vs. Professor ComputerProfessor MemoryHuge (> 60GB)Can’t remember 10 names Computing Speed Fast (> 2 billion/second)Slow (needs fingers & toes) Takes direction Does exactly as toldStill leaves the toilet seat up Speed of updates Nearly instantaneousStill wears t-shirts from 1987 Ability to plan/reason Cannot make plans; No reasoning (lacks common sense) Makes (semi-)complicated plans; Good reasoning skills (but lacks common sense)

4. People vs. Computers People: good at reasoning & analyzing  Often have trouble evaluating all possibilities Cannot consider all the different data combinations Slow computing outcome of all decision outcomes Computers: quickly do simple tasks  Have lots of memory and are good at math  But lack concept of future, ability to plan, determine best choice from range of options

5. Spreadsheets present a grid in which data can be entered  We call each location a cell  Normally name cells using their row and column Just like in game of “Battleship”  Each cell can contain a label, value, or an equation Spreadsheet B2 C4 A5

6. Using Cells Easiest way to use cell is to enter a value  Can be a number like 4, -1, or 56.2271  Can be a label like Tutors, Interest Rate, Average, or Lbs. of Raw Beef Consumed  Can be an equation All equations must begin with = Can then use +, -, *, / to do simple arithmetic More complex calculations are also possible using functions included in spreadsheet

7. Spreadsheet Calculations Power of spreadsheet comes from ability to use cells within an equation  Use cell’s name to mean the value of that cell  So to add the values in cell A2 and A3 type: = A2 + A3 Can even use result of equation within another equation  Spreadsheet does not differentiate cells containing equations or values

8. Spreadsheet Usefulness Cells display current results  When a cell’s value changes, the spreadsheet immediately recomputes equations using that cell  Also reevaluates equations which rely on those automatically propagates values And cells that use this second set of updates, and cells that use those cells… Updates are automatic and very quick!

9. Spreadsheet Differences Every Spreadsheet program is unique  Have different names for some functions  Include/not include identical functions  Specify equations in other manners  Use different characters to specify ranges But rare for normal people to find these differences

10. Common Spreadsheet Functions AVERAGE(cells) Computes mean of the values in the cells MIN(cells) Determines smallest numerical value in cells MAX(cells) Returns largest number in the cells COUNT(cells) Calculates how many cells actually contain a value

11. Common Spreadsheet Functions SUM(cells) Computes sum of the values in the cells IF(test,TRUE_VALUE,FALSE_VALUE Performs test; if test is true, it evaluates and returns TRUE_VALUE, otherwise it computes and returns FALSE_VALUE

12. Circular References Circular reference exists when a cell’s value depends on its own value  For example if we defined cell C2 as: = D2 + C2  Spreadsheet would have to update cell C2 whenever the value in cell C2 changes Circular references would force programs to recompute a cell’s value forever

13. Circular References May occur through multiple cell definitions  B2 = F2 - 1 C2 = B2 - 2 D2 = C2 * 2 E2 = D2 / 2 F2 = E2 + 2  Creates infinite cycle of updates: B2  C2  D2  E2  F2  B2  C2  D2  E2  F2

14. Spreadsheet Benefits In addition to normal uses, dynamic nature of spreadsheets enables what-if analyses:  What if I charge 10% more per murder?  What if drug cartel reduces shipments by 50%  What if I double my profit per widget?  What if we threw a war and no one came? (Probably not this last one)

15. For Next Lecture Get excited about programming and start reading handout Complete and submit homework #3  E-mail me/visit my office if you have questions Start looking over topics where you are still uncertain  Clarify thoughts with me/classmates/tutors  Midterm will be here sooner than you think