CS 7: Introduction to Computer Programming Algorithms

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”

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?

1 GL Example 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!

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

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

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)

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

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

Algorithms

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

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

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

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

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

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

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

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

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

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

Hokey Pokey - Flowchart

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

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)

References Deitel, H.M., and Deitel, P.J. Java: How to Program, 3 rd edition. Chapter 4,5 Wikipedia. 4ges.html 4ges.html