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cs2010 Notes: 26 Semester Review

··3 mins

Final Exam info: #

  • Wed Dec 11 @ 8am - 10:30am

Semester Review #

What’s a computer? #

  • Could be broadly defined, but
  • “A programmable electronic device”

What is computer science?

  • The study of computer programs.
  • What can they do?
  • What can’t they do?
  • How do you write them?

Parts of a Computer #

Conceptual Model

  • CPU
  • RAM
  • Storage
  • I/O devices

Data #

Computers typically store data as binary digits (bits), which are typically described as either a zero or one. In hardware, differentiating zero volts vs more than zero volts is easier than distingushing different voltage levels.

One or more bits can be used to represent values that are interesting to users are programmers.

If that value is an integer than can be only zero or one or a boolean value (true / false), then how bit values map to domain values is pretty obvious.

For anything more complex, you need some scheme for encoding values.

Encoding integers:

  • Fixed number of bits.
  • Binary number.
  • Place value
  • Complication: Byte ordering, endianness

More complicated:

  • Encoding two integers.
  • Encoding an array of integers (C vs Java {size, …data})
  • Encoding a string (C vs. Java)
  • Encoding an image.

Algorithms #

A well-orderecd collection of unabigiously and effectively computable operations that, when executed, produces a result and halts in a finite amount of time.

  • Well-ordered collection?
  • Effectively computable?
  • Produces a result?
  • Halts in finite time?

Ways to express algorithms #

You can try to express an algorithm as text, but it’s likely to be unclear.

More clear ways to specify the steps exactly include:

  • Pseudocode
  • Flowcharts
  • Code

Boolean Logic #

  • Basic operators: AND (ยท), OR (+), NOT (')
  • Truth tables

Uses of boolean logic:

  • Logic and conditions in computer programs (e.g. in an if statement)
  • Digital circuit design

Base Conversions #

  • We typically use base-10 numbers.
  • Computers typically store data as binary numbers.
  • Representing binary numbers as hexidecimal (or octal) is convenient.
  • The exam may have a conversion problem to some other base.
  • So it’s useful to figure out how to convert bases.

Basic concept: Place-value notation.

For any base, you’ve got a digit for each power of that base, showing how many of that power you have in the number.

Examples:

  • What’s the decimal value of base 7 “325”?
  • Convert binary “10101” to base 3.

Binary Arithmetic #

  • Addition, Subtraction, Mulitplication, Division

Negative numbers: #

  • Plan A: Sign-magnitude.
    • Problem: Negative numbers need special handling for arithemtic.
  • Plan B: Two’s complement (flip all bits, add one, ignore overflow)
    • Works for addition and subtraction just like unsgined.

Logic Gates and Circuits #

  • We can represent any boolean expression as a circuit / logic diagram.

Simplification wtih K-Maps #

  • This lets us optimize boolean expressions.

Programming in JavaScript. #

  • A program is a series of statements, which run in order.
  • Some statements have associated blocks of code (in curly braces) that are executed conditionally, repeatedly, or delayed for later execution.
  • We can store values in variables to use later. The value in a variable can typically be updated / modified as the program executes.
  • Functions are a mechanism to name a block of code to be executed with some parameters; these are the basic building block of more complicated programs.
  • Code Recipe:
    • Signature
    • Names
    • Examples
    • Standard Pattern
    • Code

Examples and Assignments #

  • Graphical browser examples
  • Big homework
  • Cookie Clicker
  • Function recipe
  • Web app
  • Word Game

Networking Stuff #

  • Network Addresses
  • Protocol Layers
  • Basic Security Stuff
  • HTTP Server

New Exam Topics #

Since the midterm, we’ve covered one main topic: Programming.

There will be programming questions on the exam.

Here are three example questions:

Translate from Flowchart to code. #

/input temp/

if (temp < 50) { console.log(“cold”); } else { console.log(“not cold”); }

What does this print? #

let xs = [10, 20, 30, 40]; for (let xx of xs) { console.log(xx + 2); } console.log(xs[2]);

That’s it. Questions? #