CS 7: Introduction to Computer Programming

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CS 7 Introduction to Computer Programming

• Algorithms

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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

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Trade-offs among the 5 Gs

• 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?

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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!

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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

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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

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4 GL SQL, Visual Basics 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 Basics GUI Creator is for designing
  Graphical User Interfaces (GUIs)

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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

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Algorithms
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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

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Algorithms - Representation

• How do you
• Make a peanut butter sandwich?
• Calculative a derivative?
• Find a job?
• Do the hokey pokey?

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Hokey Pokey List of Steps Representation

• Volunteers?
• Anything unclear in the steps the song gives?

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Flowchart symbols

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

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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

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Sequence

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

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Selection

• Single Selection (if)
• If youve won the lottery
• raise your hand
• Double Selection (if-else)
• If youre happy
• smile
• else
• frown

True
Won lottery?
Raise Hand
False
True
False
Happy?
Smile
Frown
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Selection (continued)

• Multiple Selection (switch)
• If the light is ...
• red -gt stop
• green -gt go
• yellow -gt slow down

True
Light Red?
Stop
False
True
Light Green?
Go
False
True
Light Yellow?
Slow Down
False
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Repetition

• While
• Do-while

while its 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
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Repetition (continued)

• For

Counter 1
Teaching a baby to count from 1 to 10 counter
1 if counter lt 10 increment counter print
counter number
Add 1 to counter
True
Counter 10?
Print counter
False
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Hokey Pokey - Flowchart
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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 gt 0 and count lt 21
• add 10 to counter
• return counter value

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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)

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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