CS 180 Recitation

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CS 180 Recitation
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Reminders Information

• No Lecture Monday (MLK Holiday)
• Labs/recitations as normal next week
• Class website http//web.ics.purdue.edu/cs180/S
  pring2006Web/
• Class Newsgroup
• purdue.class.cs180
• Follow the newsgroup for project information and
  questions newsgroup postings from GTAs are
  official. Even if you dont follow the newsgroup
  you are responsible for all updates/changes to
  any projects mentioned there.

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Reminders Information

• Discussion Groups
• Facilitated by Barry Wittman
• Once or twice a week (TBD) discussion of CS180
  related material
• Extra credit 1/3 point (max of 5 total for the
  semester) for each session attended
• First session Monday, January 23 (tentative),
  time/location TBD
• Look for more information in lecture recitation
  next week and on the class newsgroup

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Computer Basics

• Computer system hardware software
• Hardware the physical components
• Software the instructions that tell the hardware
  what to do

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File System
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Binary Versus Text Files

• All data and programs are ultimately just zeros
  and ones
• each digit can have one of two values, hence
  binary
• bit is one binary digit
• byte is a group of eight bits
• Representing Numbers the bits represent a number
  (each individual bit is a power of 2)
• 13 1101b 1x23 1x22 0x21 1x20
• 49 00110001b
• 180 10110100b
• Representing Text the bits represent printable
  characters
• one byte per character for ASCII, the most common
  code
• For example 65 01000001b A

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Testing and Debugging

• Even with careful programming, your code could
  still contain errors and must be thoroughly
  tested.
• Buga mistake in a program
• Debuggingfinding mistakes in a program and
  (possibly) fixing them

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Types of Errors

• Syntax
• Run-Time
• Logic

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Syntax

• The set of grammar rules for a programming
  language is called the syntax.
• The compiler checks your program to make sure it
  is a valid Java program.
• If your program is not a valid Java program, then
  the compiler outputs a message indicating a
  syntax error.

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Syntax Errors

• caught by compiler (compiler-time error)
• automatically found, usually the easiest to fix
• cannot run code until all syntax errors are fixed
• error message may be misleading
• Example
• Misspelling a command, for example rturn
  instead of return

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Run-Time Errors

• An execution error (during run-time)
• Not always so easy to fix
• Error message may or may not be helpful
• Not detected by the compiler.
• Example
• Division by zero - if your program attempts to
  divide by zero it automatically terminates and
  prints an error message.

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Logic Errors

• Just because it compiles and runs without getting
  an error message does not mean the code is
  correct!
• An error in the design (the algorithm) or its
  implementation
• code compiles without errors
• no run-time error messages
• but incorrect action or data occurs during
  execution
• Generally the most difficult to find and fix
• Need to be alert and test thoroughly
• think about test cases and predict results before
  executing the code

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Logic Error Examples

• Algorithm Error
• averageOfFiveScores SumOfScores/2(should
  divide by 5)
• Implementation Error
• typed in wrong symbol in source code -sum a -
  b(should be sum a b)

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Applets vs. Java Applications

• Applets
• Java programs intended to be downloaded via the
  Web and run immediately
• little applications
• requires a web browser
• Applications
• Java programs intended to be installed then run
• often larger applications
• Slightly different programming for each, but both
  are easy to do
• Applet example http//www.willamette.edu/gorr/cl
  asses/cs130/lectures/BinaryConversion/convert.html
  

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Operating System

• A computer program that controls the components
  of a computer system and facilitates the
  operation of applications
• Examples
• Windows
• MacOS
• Unix
• Linux
• Solaris