Computers and Programming

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Computers and Programming

• Bina Ramamurthy

127 Bell Hall bina_at_cs.buffalo.edu
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Introduction

• A computer executes the solution designed for a
  problem. A program expresses the solution in a
  form that a computer can understand.
• In this discussion we will look at the basic
  components of a computer, the programming
  environment, the system support, and program
  development phases.

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Topics for discussion

• Basic components of a computer
• Operating systems
• High level language
• Processing a program
• Software development stages
• Example

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Basic Components of a digital computer
CONTROL
INPUT
OUTPUT
PROCESSOR
MEMORY
DATA
CONTROL
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..Components ...

• Processor Arithmetic Logic Unit (ALU)
• ALU Control CPU Central Processing Unit
• Ex PowerPc 604, Intel Pentium, Motorola 68xxx
• Ex Input Mouse Output laser printer
• Memory main memory (RAM)
• Secondary memory Floppy disk, hard disk.

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Operating systems

• Provides user interface
• Resource management
• Security and protection
• Provides utility programs and libraries Editor,
  math library
• Example unix , MS-DOs, windows-95

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High level language

• The hardware underlying a computer communicates
  and computes in binary code called machine code.
• But in order for the humans to effectively
  communicate the solutions to a computer we need a
  language that is closer to human language High
  Level language (HLL). ex C
• Problem HLL --gtmachine code
• Solution A translation mechanism Compiler or
  an interpreter

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Steps in software development

• Problem analysis
• Clear understanding of the problem
• identify problems input, output, requirements
  and constraints.
• Solution design
• Class design Identify the classes of objects
  required by the problem and draw relationship
  among these.
• Algorithm design Stepwise solution to carry out
  the functionality of the classes.

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Steps in software development (contd.)

• Documentation
• Provide information for use and maintenance of
  the software. Provide an example that gives input
  and output.
• Implementation
• Code the algorithms into a programs using a HLL.
• Debugging
• Compile and execute the software. Remove any
  errors.
• Testing
• Execute with various test data and make sure the
  software works as expected.

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Example (non-computer problem)

• Problem 1 You are on your way to visit a friend
  in Chicago. You are driving in downtown Chicago
  and are lost. Solve this problem.

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Example (computer problem)

• Problem 2 Count the number of times the letter
  a occurs in a piece of text.
• Solution
• 1. Initialize Acounter 0 // Assignment -
  memory
• 2. Input a character from input. //input
• 3. If it is an a then // selection
• Increment Acounter // arithmetic -
  memory
• 4. Repeat steps 2 - 3 until end of input.
  //repetition
• 5. Output Acounter. // output
• 6. Exit