CMPT 120

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CMPT 120

• Introduction to Computer Science and Programming
  I
• Chris Schmidt

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CMPT 120

• What will you learn?
• Basic concepts of Computing Science
• How computers store some types of data
• Algorithms (methods of solving problems)
• Data Structures (how to store complex data)
• How to analyze and compare algorithms
• How to write programs in Python

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Computing Science

• Comput-ing Science
• The majority of the time we arent concerned with
  the computer itself (hardware)
• The main concern is the creation, analysis, and
  application of algorithms
• Hard to pin down a good definition

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Computing Science

• Computing Science is an extremely diverse field
  ranging from the completely theoretical to the
  very practical
• Logic, Complexity and Computability, Database
  Management, Artificial Intelligence,
  Human-Computer Interaction, Graphics, Natural
  Language Processing, Operating Systems,
  Programming Languages, Networking,
  Bioinformatics, Computer Architecture, Software
  Engineering

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The Basics

• Hardware
• Physical equipment (processor, monitor, keyboard,
  printer)
• If you can touch it, its hardware
• Software
• Programs (sets of instructions) that run on the
  hardware

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Hardware

• Some Basic Computer Components
• CPU Central Processing Unit
• The computers central brain
• ALU Arithmetic and Logic Unit
• Memory
• ROM Read Only Memory
• RAM Random Access Memory
• Storage
• Hard Disk, CD-Rom, etc.
• Input
• Keyboard, Mouse
• Output
• Monitor, Printer

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Software

• Computer Program
• A set of instructions that the computer will
  complete
• The instructions that are used are defined by a
  programming language

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Programming Languages

• High Level Languages
• The languages you usually here about are high
  level languages (Python, C, Java, Visual
  Basic..
• These languages are used to write the everyday
  applications we see
• Use complex instructions that cant be directly
  understood by a computers hardware

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High Level Code (Python)

• metres float(raw_input( \ "Enter your height
  (in metres) "))
• total_inches 39.37 metres
• feet int(total_inches/12)
• inches total_inches - feet12
• print "You are " str(feet) " feet and " \
  str(inches) " inches tall."

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Programming Languages

• Machine Language
• Processors have a small set of simple
  instructions they understand
• Access/store a value, add two values, compare two
  values,
• Different processor types have different
  instructions
• Each instruction is identified by a unique number

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Programming Languages

• Assembly Language
• Machine language is difficult for humans to work
  with directly (its all numbers)
• Assembly Language is one step higher
• The instructions are given short names
  (mnemonics) so it is readable
• A compiler converts the text of a program in
  assembly language into the appropriate Machine
  Language

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Assembly Language Code

• ORG 0000
• N1 DB 11110100
• N2 DB !41
• ANS1 RMB 1
• ANS2 RMB 1
• ORG 0010
• START LDS 00FF
• LDD !0
• LDX !0
• LDY !0
• PSHA
• LDAA N1
• PSHA
• .
• .

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Programming Languages

• Back to High Level Languages
• Instead of using the simple instructions of
  assembly language we work with more readable high
  level languages
• As with assembly language a compiler or
  interpreter is needed to convert the code to the
  machine language

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Python

• Interpreted vs Compiled
• Compiled languages (C, Java) are written as
  text and then must be compiled into machine code
• Interpreted languages (Python) are written as
  text, but do not need to be compiled. When run,
  an interpreter, converts the code line by line

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Advantages

• Compiling
• Faster at runtime, no translation to machine code
  needed
• Interpreting
• More flexibility when editing, dont have to
  recompile every time you want to test a change
• More flexible at runtime (though we probably
  wont take advantage of this in 120)

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Hello World!

• The first program people often write simply tells
  the computer to print the phrase Hello World!
• The simplicity of a language can be seen to some
  extent by how complex the code needed to do this
  is.

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Hello World!

• Python
• print "Hello World!"
• C
• include ltiostreamgt
• using namespace std
• int main ()
• cout ltlt "Hello World!"
• return 0
• Java
• public class HelloWorld
• public static void main(String args)
• System.out.print("Hello World!")

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Python Powers of Two

• print "The first ten powers of 2."
• x1
• for i in range(10)
• print x,
• xx2

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C Powers of Two

• include ltiostreamgt
• using namespace std
• int main ()
• int x 1
• cout ltlt "The first ten powers of 2.\n"
• for (int i0 i lt 10 i)
• cout ltlt x ltlt " "
• x x2
• return 0