CS 7: Introduction to Computer Programming

1. CS 7: Introduction to Computer Programming Algorithms

2. Review • What are the 5 generation languages (“GL”)? • 1 GL – machine language • 2 GL – assembly language • 3 GL – high level language • 4 GL – “non-procedural, specification language” • 5 GL – “constraint-based, Artificial Intelligence language”

3. Trade-offs among the 5 G’s • Productivity • Time to write, debug, maintain code • Portability • Ease of taking program written on 1 computer and moving it to another • Efficiency • Time it takes code to run • Amount of space it takes to run • Task Dependent • Is the language developed for a specific task?

4. 1 GL • Example • 000000 00001 00010 00110 00000 100000 • Add registers 1 and 2, place result in register 6 • Low productivity • Lots of instructions needed for simple tasks • Low portability • Different machine languages for different architectures • High efficiency • can take advantage of architecture dependent features • can write more quick and compact code • Not task dependent • Everything ultimately must be in machine code!

5. 2 GL - MIPS • Example • add $1, $2, $6 • Add registers 1 and 2, place result in register 6 • Low productivity • Lots of instructions needed for simple tasks • Usually 1-to-1 correspondence with machine language • Easier to read • Low portability • Different machine languages for different architectures • High efficiency • can take advantage of architecture dependent features • can write more quick and compact code • Not task dependent

6. 3 GL – Java, C++, BASIC, FORTRAN • Example • d = e + f; • Add the values in e and f, place result in d • High productivity • 1 instruction can be 100, 1000 lines of machine code • Much more like human language • Highly portable • Run on any machine with necessary compiler, interpreter • Efficiency • Not as good as machine code • Not task dependent

7. 4 GL – SQL, Visual Basic’s GUI Creator • Example • FIND ALL RECORDS WHERE NAME IS “HOFFMANN” • High productivity • Easy than 3 GL • Highly portable • Run on any machine with necessary compiler, interpreter • Efficiency • Not as good as machine code or high level language • Task dependent • SQL used for database queries • Visual Basic’s GUI Creator is for designing Graphical User Interfaces (GUIs)

8. 5 GL – Prolog, Neural Networks • Example • Specify neural network architecture for learning to map written character to ASCII equivalent • High productivity • Highly portable • Efficiency • Not as good as machine code or high level language • Task dependent • Used to solve problems with specific constraints

9. Some Notes • Syllabus • Typo (5 not 6 projects) • Make sure to read all of the relevant sections of book for the week before the first lecture of that week • Labs start today

10. Algorithms

11. Algorithms - Definition • Set of instructions used to complete a task • Can be represented as • Pseudocode – list of steps, is precise but not implemented in programming language • Flowchart – graphical representation

12. Algorithms - Representation • How do you… • Make a peanut butter sandwich? • Calculative a derivative? • Find a job? • Do the hokey pokey?

13. Hokey Pokey – List of Steps Representation • Volunteers? • Anything unclear in the steps the song gives?

14. Flowchart symbols • Action Symbol • Instructions changing a state • Decision Symbol • Instructions testing a state • Flowline • Instructions transferring to next step • Start/End Symbol

15. Control Structures • Bohm & Jacopini showed all programs could be written in terms of 3 structures: • Sequence – which instruction should be done next? • Selection – select between options • Repetition – repeat an action while a given condition stays true

16. Sequence • 1) Open the jar • 2) Scoop out the peanut butter • 3) Spread the peanut butter on the bread

17. Selection • Single Selection (if) • If you’ve won the lottery: raise your hand • Double Selection (if-else) • If you’re happy: smile else: frown True Won lottery? Raise Hand False False True Frown Happy? Smile

18. Selection (continued) • Multiple Selection (switch) If the light is ... red -> stop green -> go yellow -> slow down True Light Red? Stop False True Light Green? Go False True Light Yellow? Slow Down False

19. Repetition • While • Do-while while it’s still clumpy Stir the mixture True Mixture Clumpy? Stir False ask parents if must eat vegetables while parents say “Yes” Must I eat Veggies? Parent say “Yes”? True False

20. Repetition (continued) • For Counter = 1 Teaching a baby to count from 1 to 10: counter = 1 if counter <= 10: increment counter print counter number Add 1 to counter True Counter ≤ 10? Print counter False

21. Hokey Pokey - Flowchart

22. Pseudocode • Pseudocode - Algorithm written in way that resembles code: • Example (from BlackJack) method computeScore(cards): for each card in hand: if card is ace: add 1 to score add 1 to numAces else if card is face card: add 10 to score otherwise: add face value to score while numAces > 0 and count < 21: add 10 to counter return counter value

23. Algorithms - characteristics • What kinds of things are we seeing in these tasks? • They have an input, an output, and do some processing • That processing needs to terminate, be unambiguous, and simple to perform (we want to be able to easily implement it from the algorithm)

24. References • Deitel, H.M., and Deitel, P.J. Java: How to Program, 3rd edition. Chapter 4,5 • Wikipedia. • http://www.soi.city.ac.uk/~tony/dbms/4ges.html