Computer Programming Notes

What is a Computer?

• A device capable of performing computations and making logical decisions at high speeds.

• Processes data under the control of computer programs.

• Hardware includes a processing unit, memory, and I/O devices.

• Software refers to the computer programs that run on the hardware.

Hardware Aspects

Computer Organization

• Input/Output unit:

  • Monitor

  • Pointing device and Keyboard

  • Secondary storage (hard disks)

• Memory unit:

  • Read-only memory (ROM)

  • Read-Write memory (RAM)

• Central Processing Unit (CPU):

  • Arithmetic & Logic Unit (ALU)

  • Internal registers

Basic Diagram of Computer Architecture

• Includes:

  • Address Bus

  • Memory

  • CPU

  • Input

  • Output

  • Real World

  • Data Bus

  • Control Bus

Input/Output (I/O) Devices

• Functions:

  • Input Devices: Keyboards, mice, scanners, and microphones allow users to input data into the computer.

  • Output Devices: Monitors, printers, and speakers output data from the computer to the user.

• Collaboration:

  • Input devices send data to the CPU for processing.

  • The CPU sends the results to output devices.

  • The CPU communicates with I/O devices through interfaces and protocols.

Memory Unit

• Functions:

  • Storing Data: Stores data and instructions.

    • Includes volatile (RAM) and non-volatile memory (ROM, hard drives, SSDs).

  • Temporary Storage: RAM provides space for data and instructions currently in use.

    • Faster, volatile (loses data when power is off).

  • Permanent Storage: ROM stores firmware and boot instructions.

    • Storage devices (HDDs, SSDs) store data and programs permanently.

• Collaboration:

  • Provides the processor with data and instructions.

  • The CPU continuously reads from and writes to memory.

Processor (Central Processing Unit, CPU)

• Functions:

  • Executing Instructions: Fetches, decodes, and executes instructions.

    • Performs arithmetic, logical, control, and I/O operations.

  • Control Unit (CU): Directs the operation of the processor.

    • Tells memory, ALU, and I/O devices how to respond.

  • Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations.

• Collaboration:

  • Fetches instructions from memory, decodes them, and executes them.

  • Communicates with memory to retrieve and store data.

Collaboration to Complete Tasks

• Task Initiation: User inputs data via an input device.

• Data Processing: CPU fetches instructions and data from memory and processes the data.

• Intermediate Storage: CPU stores intermediate results in RAM.

• Output Generation: CPU sends final results to an output device.

• Data Management: CPU saves processed data to permanent storage.

Example: Opening a Word Processor

• User Input: User clicks on the word processor icon (mouse).

• Fetching Instructions: CPU fetches instructions from storage (HDD/SSD) into RAM.

• Execution: CPU executes the instructions to load the word processor.

• User Interaction: User types (keyboard); CPU processes keystrokes and stores in RAM.

• Saving Data: CPU writes data from RAM to storage (HDD/SSD).

• Output: Document is displayed on the monitor.

Operating System

• A layer of software that manages the computer's hardware.

• Includes the file system.

• Loaded from secondary storage at startup.

• Examples: MS Windows, UNIX, Linux, MAC OS X.

Main Functions of an Operating System

• Hardware management

• File system management

• Provides a user interface

• Executes and provides services for application software

• Data access

• System Resource management (e.g., memory)

• System security (access control)

• Network communications (share resources)

Computer Configurations

• Hardware configurations:

  • Stand-alone Personal Computing (generic PC): Desktops, Laptops, Tablets & Smartphones

  • Workstation: CAD WS, Media WS, Scientific WS

  • Server: File, Print, DB, Web, Mail, Gaming, Media, Backup, Access Control, etc.

  • Tablets and Smartphones

  • Embedded systems: IoT devices, inside appliances

  • Local Area Network (LAN)

  • Virtual machines (vmware, hyper-V)

• Software configurations:

  • Stand Alone programs

  • Client/Server applications

  • Distributed Computing

  • Web Services

  • Cloud Computing

• Future: Quantum Computers

Software Aspects

Programming Languages

• Machine language:

  • Lowest level language.

  • The only language computers understand.

• Assembly language:

  • Higher level than machine language.

  • Needs to be assembled to machine language.

• High-level language:

  • More understandable by humans.

  • Needs to be compiled for computers to understand.

Machine Language

• Defined by the computer hardware design.

• Machine dependent.

• The only code that computers understand.

• Cumbersome to work with.

• Ultimately reduced to 1’s and 0’s.

• Example:

  • $+1300042774$

  • $+1400593419$

  • $+1200274027$

Assembly Language

• Uses English-like abbreviations.

• More readily understandable to humans.

• Assemblers needed to translate assembly code to machine language.

• Cleaner to work with but still requires many instructions.

• Example:

  • LOAD BASEPAY ADD OVERPAY STORE GROSSPAY

High-Level Language

• Instructions look like everyday English phrases and contain mathematical notations.

• Single statements accomplish substantial tasks.

• Compilers and Interpreters translate high-level languages to machine language.

• Example code: grossPay = basePay + overTimePay

• Example languages: Fortran, Cobol, Pascal, Java, C, C++, Visual Basic, C#.

Code Translators

• Assemblers:

  • Translates assembly code into machine language.

• Compilers:

  • Converts HLL code into machine language.

  • Requires recompilation after code changes.

• Interpreters:

  • Provide real-time compilation of HLL source code.

  • Popular for frequent updates and corrections.

  • Slower execution than compiled programs.

VISUAL BASIC FOR APPLICATIONS (VBA)

VBA for Excel

• GUI radically changed how engineers interact with computers.

• Excel program can be viewed as a GUI.

• Facilitates data entry and produces charts using Visual Basic for Applications (VBA).

VBA Offers:

• Numerical programming functionality:

  • Loops, arrays, logical structures, etc

• Object-oriented programming features

• Easy way to send information to and from Excel worksheets

Basic Concepts

• Programs

• Assignment

• Decisions and Loops

The “idea” of a Program

• A program is a sequence of unambiguous instructions (statements).

• The computer implements instructions sequentially at a fast rate.

• Ambiguous and illogical instructions won't work properly.

Example Program in VBA

• vba Sub Adder() a = 10 b = 33 c = a + b End Sub

• Assigns numeric constants to variables a and b.

• Adds them and assigns the result to variable c.

The Concept of Assignment

• Information is represented in two ways:

  • Directly as constants: a value that does not change.

  • Symbolically as variables: a symbolic name that can take on different values.

• Constants can be assigned to variables.

Assignment Statement & Computer Memory

• A variable is a label the computer associates with a memory location.

The Assignment Operator (=)

• The equals sign means “is replaced by” or “is assigned the result”.

• Different from the conventional meaning of equality.

• Alternatives: angle  45, Pascal and MathCad adopted “:=”.

• Assignment statements must have a single variable on the left-hand side.

• Invalid VBA statements: a + b = c, 3 = x – y + 99

• Valid VBA statement: x = x + 1

• After execution, the memory location for x increments by one.

Alphanumerical Information

• Computers also process information other than numbers.

• Handle names, labels, and identification numbers (strings).

• String constants are enclosed in quotes.

• Variables storing strings are called string variables.

• Example: n = “Louis Armstrong” sets up a memory location n containing “Louis Armstrong”.

Decisions and Loops

• Ways to deviate a computer program from its sequential mode of operation.

• Decisions: If Then Else

• Loop: For Next

Decisions

• Implemented using the If-Then statement.

• Example:

  • vba If a < 0 Then s = -1 Else s = 1 End if

Loops

• A loop repeats a VBA statement(s) several times.

• The For-Next loop is the simplest way to do this.

• Example:

  • vba x = 0 n = 5 For i = 1 to n x = x + i Next i

Example: Summation or Factorial

• vba calctype = “summation” n = 5 If calctype = “summation” Then x = 0 For i = 1 to n x = x + i Next I Else x = 1 For i = 1 to n x = x * i Next i End if

• Illustrates how sequences, decisions, and loops can be combined.

Summary

• What is a computer?

• Computer organisation

• Operating system

• Computer configurations

• Programming languages

• Code translators

• VBA for Excel

• Basic Concepts

• The idea of a program

• Assignment & Memory

• Assignment operator (=)

• Alphanumeric information

• Decisions & Loops

• Example

Introduction to Computer Programming Discussion