COMP 14Introduction to Programming

Miguel A. Otaduy

May 12, 2004

…from Last Time

• Homework 1 due Tomorrow– Fill in form with personal info– Getting started with jGRASP– Compile and Run test programs

– Any problems?

– Disable test for new versions

Today (ch. 1)

• Parts of the computer– hardware vs. software– CPU and memory

• Binary numbers

• What is an algorithm?

Reading Check-Up

1. - computer components including the CPU, main memory, I/O devices, and secondary storage

2. - the brain of the computer, containing the CU, PC, IR, ALU, and ACC

3. - computer instructions to solve a problem

4. The digits 0 and 1 are calledor the shortened term

hardware

CPU

program

binary digits

bits

Hardware vs. Software

A computer is made up of hardware and software

Hardware Software• CPU

- ex: 1 GHz Pentium III• input/output

- keyboard- monitor- network card

• main memory- ex: 256 MB RAM

• secondary memory- ex: 20 GB hard drive

• operating systems- Windows XP- Mac OS X

• applications- games- Microsoft Word- Internet Explorer

Hardware Organization

motherboard

CPU

memory

hard drive

Central Processing UnitCPU• Control Unit (CU)

– "the brain" of the CPU

• Program Counter (PC)– points to the next instruction to be executed

• Instruction Register (IR)– holds the currently executing instruction

• Arithmetic Logic Unit (ALU)– carries out all arithmetic and logical ops

• Accumulator (ACC)– holds the results of the operations

performed by the ALU

Main Memory

• Ordered sequence of cells

• AKA Random Access Memory (RAM)

• Directly connected to the CPU

• All programs must be brought into main memory before execution

• When power is turned off, everything in main memory is lost

Main MemoryWith 100 Cells

Each memory cell has a numeric address, which uniquely identifies it

CPU and Main Memory

Chip that executesprogram instructions(processor)

Primary storage areafor programs and datathat are in active use(RAM)

All programs must be brought into main memory before execution

Secondary Storage

• Provides permanent storage for information• Retains information even when power is off• Examples of secondary storage:

– Hard Disks– Floppy Disks– ZIP Disks– CD-ROMs– Tapes

Secondary Storage

Secondary memorydevices providelong-term storage

Information is movedbetween main memoryand secondary memoryas needed

Input Devices

• Definition: devices that feed data and computer programs into computers

• Examples:– Keyboard– Mouse– Secondary Storage

Output Devices

• Definition: devices that the computer uses to display results

• Examples:– Printer– Monitor– Secondary Storage

Input/Output Devices

I/O devices facilitateuser interaction

Hardware Components

Opening MS Word• Use the mouse to

select MS Word• The CPU requests

the MS Word application

• MS Word is loaded from the hard drive to main memory

• The CPU reads instructions from main memory and executes them one at a time

• MS Word is displayed on your monitor

Questions

1. - points to the next instruction to be executed

2. - a unique location in memory

3. - stores information permanently

4. Instructions executed by the CPU must be first loaded to

program counter (PC)

address

secondary storage

main memory

Software Categories

• Operating System– controls all machine activities– provides the user interface to the computer– first program to load when a computer is

turned on– manages computer resources, such as the

CPU, memory, and hard drive– examples: Windows XP, Linux, Mac OS X

• Application– generic term for any other kind of software– examples: word processors, missile control

systems, games

Operating System (OS)

• OS monitors overall activity of the computer and provides services

• Written using programming language

• Example services:– memory management– input/output– storage management

Application Programs

• Written using programming languages

• Perform a specific task• Run by the OS• Example programs:

– Word Processors– Spreadsheets– Games

Questions

Classify the following pieces of software as operating system or application:

1. Microsoft Windows 20002. Microsoft PowerPoint3. Linux4. Your COMP 14 programs

OS

OS

app

app

It’s All About Data

• Software is data– numbers, characters– instructions, programs

• Hardware stores and processes data– read, write– add, subtract, multiply, divide

Analog vs. Digital

• Analog– continuous wave forms– ex: sound, music on an audio tape

• Digital– the information is broken down into pieces,

and each piece is represented separately– represented as series of 0 and 1

• 0 - low voltage• 1 - high voltage

– can be copied exactly– ex: music on a compact disc

H i , H e a t h e r .

72 105 44 32 72 101 97 116 104 101 114 46

Representing Text Digitally• All information in a computer is

digitized, broken down and represented as numbers.

Corresponding upper and lower case Corresponding upper and lower case letters are separate characters.letters are separate characters.

Language of a Computer• Machine language: the most basic

language of a computer

• A sequence of 0s and 1s– binary digit, or bit– sequence of 8 bits is called a byte

• Every computer directly understands its own machine language– why can't Windows programs run on Apple

computers?

1 bit01

2 bits

00011011

3 bits

000001010011100101110111

4 bits

00000001001000110100010101100111

10001001101010111100110111101111

Each additional bit doubles the number of possible permutations

Bit Permutations

21 = 2 items

22 = 4 items

23 = 8 items

24 = 16 items

25 = 32 items

1 bit ?

2 bits ?

3 bits ?

4 bits ?

5 bits ?

How manyitems can be

represented by

Bit Permutations

• Each permutation can represent a particular item

• There are 2N permutations of N bits– N bits are needed to represent 2N

unique items

Binary Numbers

• N bits to represent 2N values• N bits represent values 0 to 2N-1• Example: 5 bits

– 32 unique values (0-31)– 00000 = 0– 11111 = 31

24 23 22 21 20

16 + 8 + 4 + 2 + 1

Decimal to Binary

114 1110010

Place Digit Value26 1 64

25 1 3224 1 1623 0 022 0 021 1 220 0 0

QuestionsBinary Numbers

• What’s the maximum value a 6-bit number can represent?

• What’s the decimal representation of 111010?

• What’s the binary representation of 35?

63

58 = 32+16+8+2

100011

KB 210 = 1024

MB 220 (over 1 million)

GB 230 (over 1 billion)

TB 240 (over 1 trillion)

Unit Symbol Number of Bytes

kilobyte

megabyte

gigabyte

terabyte

Storage Capacity

• Every memory device has a storage capacity, indicating the number of bytes (8 bits) it can hold

• Various units:

Programming LanguagesEvolution• Early computers programmed in

machine language (only 0s and 1s)

• Assembly languages were developed to make programmer’s job easier

• Assembler: translates assembly language instructions into machine language

Assembly and Machine Language

Programming LanguagesEvolution

• High-level languages make programming easier

• Closer to spoken languages• Examples:

– Basic – FORTRAN– COBOL– C/C++– Java

From Java to Machine Language• Computers understand only 0 and 1 (machine

language)• Compiler translates source code into machine

code

• Java compiler translates source code (file ending in .java) into bytecode (file ending in .class)– bytecode is portable (not machine-specific)

• Java interpreter reads and executes bytecode– different Java interpreters for different types of CPUs

and operating systems (OS)• Intel/Windows, Motorola/Mac OS X, Intel/Linux

Problem Solving• The purpose of writing a program is to solve a

problem

• The general steps in problem solving are:– understand the problem– dissect the problem into manageable pieces– design a solution– consider alternatives to the solution and refine it– implement the solution– test the solution and fix any problems that exist

Algorithm

• Sequence of instructions used to carry out a task or solve a problem

• May be written in either English or pseudocode– outline of a program that could be

translated into actual code

• May need refinement as you work

Always write out your algorithm before you begin programming

Problem-Analysis-Coding-Execution

most important stepwithoutcomputer

withcomputer

Algorithm Design Example

Problem: Convert change in cents to number of half-dollars, quarters, dimes, nickels, and pennies to be returned.

Example: – given 646 cents– number of half-dollars: divide 646 by 50

• quotient is 12 (number of half-dollars)• remainder is 46 (change left over)

– number of quarters: divide 46 by 25• quotient is 1 (number of quarters)• remainder is 21 (change left over)

– number of dimes, nickels, pennies– result: 12 half-dollars, 1 quarter, 2 dimes, 0

nickels, 1 penny

Resulting Algorithm

1. Get the change in cents2. Find the number of half-dollars3. Calculate the remaining change4. Find the number of quarters5. Calculate the remaining change6. Find the number of dimes7. Calculate the remaining change8. Find the number of nickels9. Calculate the remaining change10.The remaining change is the number of

pennies.

Exercise

• Execution of c=2*a+b in a computer

To do

• Read ch. 2• Exercises 10 & 11 in ch. 1

(algorithm design)

What’s Ahead...

• Java Basics

• Homework 1 due tomorrow• Homework 2 assigned tomorrow

• Quiz Friday: computers and Java basics