HOW COMPUTERS MANIPULATE DATA

Chapter 1 HOW COMPUTERS MANIPULATE DATA Coming up: Analog vs. Digital

Hardware and Software • Hardware • the physical, tangible parts of a computer keyboard, monitor, disks, wires, chips, etc. • Software • programs and data • a program is a series of instructions • A computer requires both hardware and software; otherwise useless without the other

Digital Information • Computers store all information digitally: • numbers • text • graphics and images • video • audio • program instructions • In some way, all information is digitized - broken down into pieces and represented as numbers Coming up: Representing Text Digitally

72 105 44 32 72 101 97 116 104 101 114 46 Representing Text Digitally H i , H e a t h e r . For example, every character is stored as a number, including spaces, digits, and punctuation Corresponding upper and lower case letters are separate characters Coming up: Binary Numbers

Binary Numbers Once information is digitized, it is represented and stored in memory using the binary number system A single binary digit (0 or 1) is called a bit Devices that store and move information are cheaper and more reliable if they have to represent only two states A single bit can represent two possible states, like a light bulb that is either on (1) or off (0) Permutations of bits are used to store values Coming up: Bit Permutations

1 bit 2 bits 3 bits 4 bits 0 1 00 01 10 11 000 001 010 011 100 101 110 111 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Bit Permutations Each additional bit doubles the number of possible permutations Coming up: Bit Permutations

1 bit ? 2 bits ? 3 bits ? 4 bits ? 5 bits ? How many items can be represented by Bit Permutations 21 = 2 items 22 = 4 items 23 = 8 items 24 = 16 items 25 = 32 items Each permutation can represent a particular item There are 2N permutations of N bits Therefore, N bits are needed to represent 2N unique items Coming up: Java and Unicode

Java and Unicode How do we map from numbers to characters? In Java we use the Unicode specification which maps each character to a 16-bit number. So, how many possible characters can we have? 216 = 65536 ASCII is an older set that was 8-bits and thus could represent only 28=256 Note: The creators of Unicode started with ASCII, so the 256 ASCII character codes are a subset of Unicode Coming up: Java and Unicode

Java and Unicode • Unicode is International… and includes our alphabet, but many other countries (Russian, Asian, Arabic, etc…). • For our alphabet we need both upper and lower case representations! See: http://www.alanwood.net/demos/ansi.html Unicode also includes some non-printable characters like null, tab, line feed, delete,… Why 65,000 characters? We only have 26 letters! Coming up: Binary – How does the computer see numbers?

Binary – How does the computer see numbers? Computers represent information digitally, but only using a series of 1s and 0s. Binary = Base 2 Decimal = Base 10 Hexadecimal = Base 16 Coming up: Decimal Numbers (normal)

Decimal Numbers (normal) Place 0 means multiple by <base>0 In this case 100 = 1 Place 1 means multiply by <base>1 In this case 101 = 10 So 23 = 101*2 + 100*3 = 23 Place 0 Place 1 In decimal (base 10) we represent a number between 0-9 with one digit. To get any higher we use another position 23 Coming up: Binary Conversions

Binary Conversions 22*1+21*0+20*1 = 4*1 + 2*0 + 1*1 = 5 in decimal = Place 2 Place 0 Place 1 5037 = 103*5 + 102*0 + 101*3 + 100*7 Now, what about Binary, which is Base 2? Available digits then are 1 and 0 only. Binary 101 is what in decimal? Coming up: Binary Conversions

Joke There are only 10 kinds of people in this world. Those who know binary and those who don’t. Coming up: Hexadecimal – base 16

Hexadecimal – base 16 • Base sixteen means we need 16 digits.. 0-9 is 10 digits, how do I get more? A,B,C,D,E,F are valid “digits” in Hex. A=10, B=11, C=12, D=13, E=14, F=15 • So, a hex number looks like: • 3A or FFF or A2C4B • What is 1A in decimal? • 161*1 + 160*10 = 26 decimal • Normally hexadecimal numbers are preceded by “0x” which means it is a hex number. Coming up: What is 0x20 in decimal?

How to convert from decimal to binary • Next divide the number by the place value to determine the digit for that position • 24/16 = 1 • Repeat process with remainder (8 in this example) • 8/8 = 1 • So I need a 1 in the 16 position and 8 position: • = 11000 Given a number (24) find the largest place value that is lower than the number 26 = 64 25 = 32 24 = 16 23 = 8 22 = 4 21 = 2 20 = 1 Coming up: Convert 9 into binary

Convert 9 into binary • 8 is the largest placevalue that fits inside 9, so • 9/8 = 1 • Remainder is 1 • 1 is the largest place value that fits in 1, so • 1/1 = 1 • Remainder is 0 • 1001 = 9 26 = 64 25 = 32 24 = 16 23 = 8 22 = 4 21 = 2 20 = 1 Coming up: Convert 7 into binary?

Convert 35 to hexadecimal • 16 is the largest placevalue that fits inside 35, so • 35/16 = 2 • Remainder is 3 • 3/1 = 3 • Remainder is 0 • 0x23 = 35 163=4096 162=256 161=16 160=1 Coming up: Conclusions

Conclusions You should understand the math to do conversions to/from binary/decimal/hexadecimal We’ll use this later in a project and lab. You may even see a question on it on the exam End of presentation

Java • A programming language specifies the words and symbols that we can use to write a program • A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements • It was introduced in 1995 and it's popularity has grown quickly since

Java Program Structure • In the Java programming language: • A program is made up of one or more classes • A class contains one or more methods • A method contains program statements • A Java application always contains a method called main • See HelloWorld.java

Java Program Structure // comments about the class public class HelloWorld { } class header class body Comments can be placed almost anywhere

Java Program Structure // comments about the class public class HelloWorld { } // comments about the method public static void main (String[] args) { } method header method body

Identifiers • An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign • Identifiers cannot begin with a digit • Java is case sensitive - Total, total, and TOTAL are different identifiers • By convention, programmers use different case styles for different types of identifiers, such as • title case for class names - Lincoln • upper case for constants - MAXIMUM

Program Development • The mechanics of developing a program include several activities • writing the program in a specific programming language (such as Java) • translating the program into a form that the computer can execute investigating and fixing various types of errors that can occur • Software tools can be used to help with all parts of this process

Language Levels • There are four programming language levels: • machine language (CPU specific) • assembly language • high-level language • fourth-generation language • The other levels were created to make it easier for a human being to read and write programs

Programming Languages • Each type of CPU executes only a particular machine language • A program must be translated into machine language before it can be executed • A compiler is a software tool which translates source code into a specific target language • Often, that target language is the machine language for a particular CPU type • The Java approach is somewhat different

Java Translation • The Java compiler translates Java source code into a special representation called bytecode • Java bytecode is not the machine language for any traditional CPU • Another software tool, called an interpreter, translates bytecode into machine language and executes it • Therefore the Java compiler is not tied to any particular machine • Java is considered to be architecture-neutral

Syntax and Semantics • The syntax rules of a language define how we can put together symbols, reserved words, and identifiers to make a valid program • The semantics of a program statement define what that statement means (its purpose or role in a program) • A program that is syntactically correct is not necessarily logically (semantically) correct • A program will always do what we tell it to do, not what we meant to tell it to do

Errors • A program can have three types of errors • The compiler will find syntax errors and other basic problems (compile-time errors) • If compile-time errors exist, an executable version of the program is not created • A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors) • A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)

errors errors Basic Program Development Edit and save program Compile program Execute program and evaluate results

Problem Solving • The purpose of writing a program is to solve a problem • Solving a problem consists of multiple activities: • Understand the problem • Design a solution • Consider alternatives and refine the solution • Implement the solution • Test the solution • These activities are not purely linear – they overlap and interact

Problem Solving • The key to designing a solution is breaking it down into manageable pieces • When writing software, we design separate pieces that are responsible for certain parts of the solution • An object-oriented approach lends itself to this kind of solution decomposition • We will dissect our solutions into pieces called objects and classes

Object-Oriented Programming • Java is an object-oriented programming language • As the term implies, an object is a fundamental entity in a Java program • Objects can be used effectively to represent real-world entities • For instance, an object might represent a particular employee in a company • Each employee object handles the processing and data management related to that employee

Objects • An object has: • state - descriptive characteristics • behaviors - what it can do (or what can be done to it) • The state of a bank account includes its current balance • The behaviors associated with a bank account include the ability to make deposits and withdrawals • Note that the behavior of an object might change its state

Classes • An object is defined by a class • A class is the blueprint of an object • The class uses methods to define the behaviors of the object • The class that contains the main method of a Java program represents the entire program • A class represents a concept, and an object represents the embodiment of that concept • Multiple objects can be created from the same class

A class (the concept) An object (the realization) Bank Account John’s Bank Account Balance: $5,257 Bill’s Bank Account Balance: $1,245,069 Multiple objects from the same class Mary’s Bank Account Balance: $16,833 Objects and Classes

HOW COMPUTERS MANIPULATE DATA