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• Computer Programming-1 is often referred to as CSC 111
• Chapter 1 contains introductory information

Chapter Outline

• Defines what a computer is
• Defines what a computer program is
• Defines the programmer's algorithm
• Explains how Java programs are converted into the form a computer can understand
• Lists the characteristics of Java

What is a Computer?

• A computer executes statements involving computations and logical decisions.
• Hardware consists of the physical devices of a computer system.
• Software comprises programs that run on computers.

Computer Organization

• A computer system has six logical units:
• Input unit (mouse, keyboard).
• Output unit (printer, monitor, audio speakers).
• Memory unit (retains input and processed information).
• Central Processing Unit (CPU) which consists of:
  • Control unit: supervises operation of other devices.
  • Arithmetic and Logic Unit (ALU): performs calculations.
• Secondary storage unit (hard drives, floppy drives).

What a Computer Program Is

• Instructions are provided to a computer to perform tasks.
• A set of instructions that tells the computer to perform specific tasks is known as a computer program.

Levels of Abstraction

• Programming occurs at several levels of abstraction:
  • Human thought.
  • Pseudo-Natural Language (English, Arabic).
  • High-Level Programming Language (C, C++, Java).
  • Machine Code.

The Programmer's Algorithm

• An algorithm is a finite sequence of repeatable instructions that produces a solution to a problem.
• The programmer's algorithm consists of:
  • Defining the problem
  • Plan the problem solution
  • Coding the program
  • Compiling the program
  • Running the program
  • Testing and debugging.

Defining the Problem in Programming

• Problems are defined in terms of Input, Output, and Processing.
  • Input consists of the data to be processed.
  • Output consists of the expected/desired results.
  • Data input and output can be identified from nouns in the problem statement.
  • Processing consists of statements to achieve task
  • Processing steps may be identified by verbs.

Input and Output

• Inputs may originate from users, files, or other programs.
• Inputs can take forms such as text, graphics, and sound.
• Outputs can take forms of numbers, text, graphics, sounds, or also commands to other programs

Example Algorithms

• Calculating the area and perimeter of a rectangle:
  • Input: Length and width
  • Processing: Area = length * width, Perimeter = 2 * (length + width)
  • Output: Area and Perimeter
• Sum and average of 5 numbers:
  • Input: Five numbers (x1, x2, x3, x4, x5)
  • Processing: Sum = x1 + x2 + x3 + x4 + x5, Average = Sum / 5
  • Output: Sum and average
• Area and perimeter of a circle:
  • Input: Radius and PI
  • Processing: Area = PI * Radius * Radius, Perimeter = 2 * PI * Radius
  • Output: Area and perimeter

Planning the Solution

• Algorithms are used to outline solution steps using English-like statements called pseudocode.

Coding the Program

• Coding involves writing the program in a formal language, called a programming language, which is comprised of:
  • A set of rules
  • Symbols
  • Special words used to write program statements
• Program is written by translating the algorithm steps into programming language statements.
• The actual program writing phase is called Source code and has a ".java" extension.

Why Coding in Programming Languages?

• Writing programs use programming languages such as C, C++, and Java.
• Programming languages are easier to understand by humans than Machine Code.

Compiling Computer Programs

• Computers only understand programs written in machine code.
• Programs must be converted into machine code for computers to run them.
• Software which translates programming language statements into machine code is called a compiler.

Programming Language Compiler

• Verifies correctness of source code conforming to language rules and flags syntax errors if rules are violated.
• Once error free, converts the course code machine code.

Platform Dependent Compiling

• Diverse hardware/operating systems (Windows, Macs, Unix) necessitate unique machine code compilation that is platform specific.

Compiling Java Programs

• Produces bytecode (a ".class" file), not machine code, from the source code (".java" file).
• Bytecode converts into machine code via Java Interpreter.

Platform Independent Java Programs Compiling

• Bytecode can run on a computer with a Java Interpreter installed.

Multipurpose Java Compiling

• Compiling is the same regardless of platform.
• Java programs are intended to be multiplatform, this compilation process supports this.

Running The Program

• The Bytecode (.class file) goes through several stages:
• Class Loader
• Bytecode Verifier
• Bytecode Interpreter

Java Virtual Machine Components

• The Class Loader stores bytecodes in memory.
• The Bytecode Verifier ensures bytecodes do not violate security requirements
• The Bytecode Interpreter translates bytecodes into machine language

Java Virtual Machine

• Comprised of the Class Loader, the Bytecode Verifier, and the Interpreter constitute (JVM).
• The JVM is platform specific.
• The interpreter translates the bytecodes into specific machine commands.

Testing

• Program output is compared with the input to confirm it conforms.
• Two types of errors:
  • Logical errors: Program runs, but provides the wrong output.
  • Runtime errors: Program ceases suddenly when the OS executes a non-accepted statement (e.g., divide by zero).

Debugging Programs

• Debugging consists of finding, then error correction

Some Characteristics of Java

• Object-Oriented: Combines data and behavior into objects.
• Provides data abstraction and encapsulation.
• Decomposes programs into cooperating objects
• Platform-independent: portable + Architecture neutral + "Write-once, run-anywhere"
• Secure: Bytecode verifier of the JVM checks/controls untrusted bytecode and controls permissions for high-level actions.