Computer Programming

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Computer Programming

• Putting the machine under our command

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Definition of a Program

• A collection of instructions that describe a
  task, or set of tasks, to be carried out by a
  computer

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Types of Computer Programs

• Firmware
• Systems Software
• Applications Software

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Programming Languages

• A programming language is an artificial language
  that can be used to control the behavior of a
  machine.

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Early Computer Programming

• The first computers were programmed by changing
  the wiring

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Programming Language Background

• John von Neumann - stored program
• Alan Turing - Turing Machine
• Alonzo Church - Lambda calculus

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First Generation Languages

• Machine level code
• Binary
• Univac IBM 701
• Add reg 1 to reg 2 place results in reg 6
• 000000 00001 00010 00110 00000 100000

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Second Generation Languages

• Assembly code
• Mnemonic code to represent instructions
• Move 61 to register named al
• mov al, 061

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Third Generation Languages

• Use English-like terms
• Compiler to translate to machine level
• Fortran, ALGOL, COBOL early examples
• COMPUTE NET-PAY GROSS-PAY - TOTAL-TAX

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Fourth Generation Languages

• More oriented toward problem solving
• State the problem, dont care how it is solved.
• Divided into categories
• SQL - Structured Query Language
• Select from Employee where Last-Name Smith

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Fifth Generation Languages

• Set of constraints rather than steps to solve
  problems
• Heuristics
• Artificial Intelligence
• Prolog
• cat(tom) - true

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Program Development Life Cycle
Step 1 Describing the Problem
Step 2 Making a Plan
Step 3 Coding
Step 4 Debugging
Step 5 Finishing the Project
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Step 1 Describing the Problem

• The problem statement is
• The starting point of programming
• A description of tasks the program is to
  accomplish
• How the program will execute the tasks
• Created through interaction between the
  programmer and the user
• The program statement includes error handling and
  a testing plan

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Parking Garage Example
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Step 2 Developing an Algorithm
Wake Up

• Algorithm development
• A set of specific, sequential steps that describe
  what the computer program must do
• Complex algorithms include decision points
• Binary (yes/no)
• Loop (repeating actions)
• Visual tools used to track algorithm and decision
  points

Check wallet for
Do I have gt 80
Yes
No
Head off to cafe
Do I have my credit card?
Yes
No
Go get gas
Yes
Go to the ATM for cash
Buy textbook
Did I get 80 from the ATM?
Go to accounting lecture
No
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Flowchart and Pseudocode
Flowchart
Pseudocode
Bold terms show actions that are common in
programming, such as reading data, making
decisions, printing, and so on.
1. Ask the user how many hours they worked
today 2. If the number of hours worked lt 8,
compute total pay without overtime otherwise,
compute total pay with overtime pay 3. Print
total pay
Underlined words are information items that
appear repeatedly in the algorithm.
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Step 3 Coding

• Coding is translating an algorithm into a
  programming language
• Generations of programming languages

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Compilation

• Compilation is the process of converting code
  into machine language
• Compiler reads the source code and translates it
  into machine language
• After compilation, programmers have an executable
  program

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Interpreter

• Interpreter translates source code into a line by
  line intermediate form
• Each line is executed before the next line is
  compiled
• Programmers do not have to wait for the entire
  program to be recompiled each time they make a
  change.
• Programmers can immediately see the results of
  changes as they are making them in the code.

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Step 4 Debugging

• Running a program to find errors is known as
  debugging
• Sample inputs are used to determine runtime
  (logic) errors
• Debugger Tool that helps programmers locate
  runtime errors

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Step 5 Finishing the Project

• Users test the program (internal testing)
• Beta version released
• Information collected about errors before final
  revision
• Software updates (service packs)
• Problems found after commercial release
• Documentation created
• User manuals
• User training

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Programming Languages
Flash / XML

• Selecting the right language
• Space available
• Speed required
• Organizational resources available
• Type of target application

ASP / JSP
JavaScript VBScript
Visual Basic
HTML
C / C
Java
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The CPU Processing Digital Information

• CPU is the brains of the computer
• Different types of CPUs
• Intel and AMD chips Used in most Windows-based
  PCs
• Apple systems use different CPU design
• Differentiating CPUs
• Processing power
• Clock speed and cache

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Instruction Set

• All commands that the CPU can execute
• Arithmetic
• Logic
• Data
• Control flow

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Instruction Set Architecture

• CISC
• Complex Instruction Set Computer
• Many different instructions
• Intel - Windows
• RISC
• Reduced Instruction Set Computer
• Fewer instructions
• Motorola/Intel - Macintosh

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The CPU Machine Cycle

• Fetch
• The programs binary code is fetched from its
  temporary location in RAM and moved to the CPU
• Decode
• The programs binary code is decoded into
  commands the CPU understands.
• Execute
• The ALU performs the calculations.
• Store
• The results are stored in the registers

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The System Clock

• Located on the motherboard
• Controls the CPUs processing cycles
• Clock cycle
• Pulse or tick
• Clock speed
• Number of pulses per second
• Measured in hertz (Hz)

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The Control Unit

• Manages the switches inside the CPU
• Is programmed by CPU designers to remember the
  sequence of processing stages for that CPU
• Moves each switch to its correct setting (on or
  off) and then performs the work of that stage

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The Arithmetic Logic Unit (ALU)

• Part of the CPU designed to perform mathematical
  operations (addition, subtraction,
  multiplication, division, etc.)
• Also performs logical OR, AND, and NOT operations
• Is fed data from the CPU registers
• Word size Number of bits a computer can work
  with at a time

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Cache Memory

• Small amount of memory located on the CPU chip or
  near it
• Stores recent or frequently used instructions and
  data
• Used for quick access by the CPU
• Different levels of cache

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Software Horror Stories

• http//www.cs.tau.ac.il/nachumd/verify/horror.htm
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