CS 115 Chapter 1

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CS 115 Chapter 1

• Overview of Programming and Problem Solving

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Chapter 1

• Every programmer needs a mental model of a
  computer
• Every program does input / process / output
• von Neumann model - the "stored program" concept

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Computer Hardware

• CPU - central processing unit
• Where decisions are made, computations are
  performed, and input/output requests are
  delegated
• Main Memory
• Stores information being processed by the CPU
  short-term (volatile)
• Secondary Memory (Mass Storage)
• Stores data and programs long-term

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Computer Hardware Components
Peripherals

• Central Processing Unit(CPU)

Control Unit
Arithmetic Logic Unit
Auxiliary Storage Device
Memory Unit(RAM Registers)
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Memory (RAM)

• a memory cell (also called a word)
• has an address, has contents
• Contents expressed in bits / bytes - binary code
• Holds a value which may be data, may be an
  instruction
• data retrieval a "copy" not a "cut"

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Memory Cells

• Address Contents

-27.2
0 1 2 3 4 5 6 . . . 999
354
0.005
-26
H
RTV 001
. . .
X
75.62
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Secondary Storage

• files - source files, data file, output file
• hard disk, floppy, CD, flash memory stick
• slower than RAM, and cheaper per byte
• usually much larger capacity than RAM
• Units of capacity - Kilobyte, Megabyte, Gigabyte,
  Terabyte

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Languages

• Machine languages
• take a step, lift arm, grasp knob, turn knob...
• Assembly languages
• LEAVE through DOOR
• High-level languages
• "get outta here!"

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Programming Languages

• Machine Language
• Most fundamental language of the computer, the
  one the CPU "understands"
• Unique for each processor type, so not "portable"
• Binary 0s and 1s that specify what to do
• 0010 0000 0000 0100
• 1000 0000 0000 0101
• 0011 0000 0000 0110

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A Program in Machine and Assembly Language
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High Level Languages

• Are portable
• Programmer writes program in language similar to
  natural language (human)
• Examples -- FORTRAN, COBOL, Pascal,
  Ada, Modula-2, C, Java
• Most are standardized by ISO/ANSI to provide an
  official description of the language

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Software Development

• Analyze and specify the problem
• Design the algorithm
• Implement in code
• Testing
• Maintenance

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Software Development

• Problem Analysis
• Identify data objects
• Determine Input / Output data
• Constraints on the problem
• Design
• Decompose into smaller problems
• Top-down design (divide and conquer)
• Develop Algorithm (Desk check)
• Algorithm refinement (Pseudocode)

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Software Development Method

• Implementation
• Converting the algorithm into programming
  language
• Testing
• Verify the program meets requirements
• System and Unit tests
• Maintenance
• All programs undergo change over time

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A Tempting Shortcut?
DEBUG
REVISE
REVISE
DEBUG
DEBUG
REVISE
Shortcut?
CODE
GOAL
TEST
THINKING
CODE
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Translators and Tools

• Assemblers for assembly languages
• Compilers for high-level languages
• IDE (integrated development environment)
• compiler
• editor (creates text format files)
• linker
• loader
• debugger

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Translation

• Syntax - the rules governing the formation of
  statements in the language
• Spelling
• Order of words, statements
• Punctuation
• Semantics meaning of the statement
• What does it DO? What action does the computer
  do when the statement is executed?

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Processing a Program

• Editor used to enter the program
• Creates source program file
• Compiler translates the source program
• Displays syntax errors
• Creates (usually) temporary object code
• Linker to combine object file with other object
  files (like library code)
• Creates final executable program (.exe)
• Loader copies exe file into RAM to be run by
  machine

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Three C Program Stages
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Ethics

• Responsibility comes with knowledge
• hacking
• piracy
• data theft and data privacy
• Responsibility to develop programs without errors

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Some C History

• 1972 Dennis Ritchie at Bell Labs designs C and
  90 of UNIX is then written in C
• Late 70s OOP becomes popular
• Bjarne Stroustrup at Bell Labs adds features to C
  to form C with Classes
• 1983 Name C first used
• 1998 ISO/ANSI standardization of C

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Objects in a hierarchy
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Some C History
Dennis Ritchie
Bjarne Stroustrup
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Problem Solving Techniques

• Ask questions -- about the data, the process, the
  output, error conditions
• Look for familiar things -- certain situations
  arise again and again
• Solve by analogy -- it may give you a place to
  start
• Use means-ends analysis -- determine the I/O and
  then work out the details

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More Problem Solving Techniques

• Divide and conquer -- break up large problems
  into manageable units
• Building-block approach -- can you solve small
  pieces of the problem?
• Merge solutions -- instead of joining them end to
  end to avoid duplicate steps
• Overcome mental block -- by rewriting the problem
  in your own words

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Case Study Converting Miles to Kilometers

• Problem  Your summer surveying job requires you
  to study some maps that give distances in
  kilometers and some that use miles. You and your
  coworkers prefer to deal in metric measurements.
  Write a program that performs the necessary
  conversion.

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Case Study

• Analysis  The first step in solving this problem
  is to determine what you are asked to do. You
  must convert from one system of measurement to
  another, but are you supposed to convert from
  kilometers to miles, or vice versa? The problem
  states that you prefer to deal in metric
  measurements, so you must convert distance
  measurements in miles to kilometers.

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Data Requirements

• Problem Input
• miles distance in miles
• Problem Output
• kms the distance in kilometers
• Relevant Formula
• 1 mile 1.609 kilometers

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Design an Algorithm that solves the problem

• Algorithm (Pseudocode)
• 1. Get the distance in miles.
• 2. Convert the distance to kilometers.
• 3. Display the distance in kilometers.
• Algorithm Refinement
• 2.1 The distance in kilometers is 1.609 times
  the distance in miles
• Desk check!

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Miles to kilometers Implementation
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Testing

• Test with input data for which you can easily
  determine the expected results
• E.g.
• 10 miles should convert to 16.09 kilometers