Calculators are used to increase speed and accuracy of numerical computations The abacus has roots dating back over 5,000 years Mechanical calculators have been relatively commonplace since late 19th century What is a computer? A mechanical or electronic device Stores, retrieves, manipulates large amounts of data (information) at high speed, with great accuracy Does not need human intervention Carries out instructions from a program

Early Computers 1945 – 1950’s: First generation computers used vacuum tubes to do internal switching needed for computations 1955: about 300 computers in the world built mostly by IBM and Remington Rand, based on vacuum tubes. Late 1950s: invention of the transistor was one of most important inventions of 20th Century computers based on the transistor are the first solid-state computers. Early 1960’s: DEC created the minicomputer (Servers) – about the size of a file cabinet. Used small packages of transistors called integrated circuits Mainframes, such as the IBM 360 are prominent in large companies and Universities.

The Personal Computer 1970s: The personal computer becomes available with invention of the microchip 1974: The microchip, along with the invention of the microprocessor led to creation of first personal computer Bill Gates and Paul Allen founded Microsoft Corporation Stephen Wozniak and Steven Jobs founded Apple Computer, Inc.

Computers Today Currently: PCs: 95% use Microsoft Windows operating system with a huge array of available software Minicomputers (servers) are still popular with small business and universities. Mainframes are in use at large corporations. Supercomputers are very powerful and specialized Used for massive computing problems by big corporations and government departments.

Components and Operations Hardware: equipment, or devices Software: programs that contain instructions which tell the computer what to do – created by programmers Hardware and software: the two major components of any computer system Major operations in a computer: Input Processing Output

Input devices: allow data to enter the computer Mouse, keyboard, scanner Output devices: allow processed data to be exported out of the computer Printer, monitor, speakers Processing: working on the data; such as: Organizing data Checking data for accuracy Mathematical or other manipulations on data Central Processing Unit (CPU): hardware that performs the tasks

Programming language: Special language (like French or German) Understood by the computer Tells the computer what to do Used by a programmer to write a program Visual Basic, Java, C#, C++, COBOL Machine language: Language of the computer Every “Programmer” language is converted to machine language Consists of bits on or off only Compiler or interpreter: Software that translates programming languages to machine language

Components of a computer Central Processing Unit (CPU) Internal memory RAM (Random Access Memory) ROM (Read Only Memory) Mass storage devices Magnetic, optical, and solid-state Input devices such as keyboard and mouse Output devices such as monitor and printer

Central Processing Unit (CPU) Often called the brain of the computer Carries out program instructions ( in memory) Performs arithmetic and logical operations Arithmetic Logical Unit (ALU) Controls other computer components (operating system) Consists of millions of transistors on a single microchip that plug into the motherboard

Internal Memory ROM: read-only memory RAM: random-access memory Contains instructions used by computer during startup Cannot be altered by computer user RAM: random-access memory Is a “scratch pad” for user as he or she works Can be read from and written to Operating System/Applications reside

Storage categories: internal and external Internal storage: Main memory, random access memory (RAM) Located inside the computer system Volatile: contents are lost when power goes down External storage: Persistent: contents are relatively permanent Floppy drive, hard drive, flash media, magnetic tape Located outside the computer system

Mass Storage Devices Magnetic storage Optical storage Hard disks, floppy disks, zip drives Hard disks are internal, others are external Optical storage CDs and DVDs Solid-state storage Flash drives plug into a USB port

Software System Software Application Software Control system resources Operating systems – Windows, DOS, Linux, UNIX, dll, utilities, drivers Application Software Interract with a user Word Processors (MS Word) Database Managers (Access) Spreadsheets (Excel) Photo Editors Web browsers, email programs (Netscape)

What is Programming? A program is a list of instructions that is executed by a computer to accomplish a particular task. Creating those instructions is programming by a programmer

Using software to translate the program into machine language: Coding the program: Select the programming language Write the instructions Using software to translate the program into machine language: Programmers write instructions in English-like high-level languages Compilers or interpreters change the programs into low-level machine language that can be executed Syntax errors are identified by the compiler or interpreter

Programming Languages Machine Languages 0110110111110111 0000000100000000 0000000100000000 Assembly Languages One programmer instruction converted to 1 machine level instruction ADD A,B High-level Languages Looks more like English words and algebraic expressions Examples of high level languages Programmer instruction converted to many machine level ADA BASIC C++ FORTRAN COBOL Java Pascal Visual Basic

Machine Language Generation Programmer written computer code Programmer written computer code Translator (Interpreter) Program (browser) Compiler Assembler One Machine Language Instruction FUNCTION Browsers netscape MS Explorer Javascript PHP ASP Many machine Language Instructions .exe file Execute Execute MS Word, Windows XP, MS Excel, Vista, MS Explorer

Writing Programs To write a program in a high-level language, you need: Appropriate software A text editor to type and edit program statements A debugger to help find errors in program code A compiler or interpreter to translate the program into machine language

Error Types Syntax: the rules governing word usage and punctuation in the language (format, recipe, formula) Logic errors are more difficult to locate than syntax errors

A program must be free of syntax errors to be run, or executed, on a computer The program will not compile or be translated A message will point out the offending instruction To function properly, the logic must be correct The program will still execute The output may be incorrect The program may exit prematurely The program may ABEND (Abnormal Termination) The program may execute with no errors/problems

Logic A program must be free of syntax errors to be run, or executed, on a computer To function properly, the logic must be correct What’s wrong with this logic for making a cake?

Programming Process Seven programming phases: Define the Problem Outline the Solution Develop the Outline into an Algorithm Test the Algorithm for Correctness Code the Algorithm in a specific language Run the program on the computer Document and maintain the program

Define the Problem: May be the most difficult phase Users may not be able to articulate their needs well User needs may be changing frequently Programmers may have to learn the user’s functional job tasks Failure to understand the problem is the major cause of most project failures If this is not correct – the rest of the project cannot be correct

Outline the Solution: Plan the high-order steps that the program will take Walk through the logic before coding by desk-checking the logic

Develop the Outline into an Algorithm: Use tools such as flowcharts and pseudocode Flowchart: a pictorial representation of the logic steps Pseudocode: English-like representation of the logic

Test the Algorithm for Correctness: Walk through the logic before coding by desk-checking the logic Make corrections to the Flowchart/Pseudocode as needed

Code the algorithm in a specific language: Select the programming language Write the instructions Using software to translate the program into machine language: Programmers write instructions in English-like high-level languages Compilers or interpreters change the programs into low-level machine language that can be executed Syntax errors are identified by the compiler or interpreter

Run the program on the computer: Test for Syntax errors (when compiling) Test for logic errors by using selected data

Document and maintain the program: Create user documentation Create technical documentation Create documentation library Monitor processing and outputs

Syntax Error Cycle

Putting the program into production Testing the program: Execute it with sample data and check results Identify logic errors and correct them Choose test data carefully to exercise all branches of the logic Putting the program into production Do this after testing is complete and all known errors have been corrected May require coordination with other related activities or software

Constant: value does not change Variable: a memory location whose contents can vary; also called an identifier Each programming language has it own rules for naming identifiers, including: Legal characters Maximum length Use of upper or lower case Variable name must be a single word, but can be formed from several words rate, interestRate, interest_rate Constant: value does not change Values that do not change while the program is running Have identifiers, and can be used like variables for calculations, but cannot be assigned new values Literal: is use of data itself (ex: pi – 3.1474)

Data Types Basic data types: Numeric data Text data Text Numeric stored by numeric variables Text data stored by string, text, or character variables – surrounded by “ “ (ie. “color”)

Types of Data Numeric Data Character data (alphanumerics) Integer data (whole numbers) 10 25 -45 0 Real (Floating point) data (numbers that have a decimal point) 23.5 -5.0 Note: 5 and 5.0 are stored differently in a computer even though they have the same value. The first, 5 is an Integer but the second, 5.0 is a Real number. Character data (alphanumerics) All the characters you can type at the keyboard The type is String or Character

Numeric data types: Integer: whole numbers only Floating-point: fractional numeric values with decimal points

Character data (alphanumerics) Numeric Data Integer data (whole numbers) 10 25 -45 0 Real (Floating point) data (numbers that have a decimal point) 23.5 -5.0 Note: 5 and 5.0 are stored differently in a computer even though they have the same value. The first, 5 is an Integer but the second, 5.0 is a Real number. Character data (alphanumerics) All the characters you can type at the keyboard The type is String or Character

Concatenation Concatenation takes two strings and joins them to create a string result The concatenation operator is symbolized, in pseudocode, with a + sign Example: if: String1 = “yellow” and String2 = “duckie” then the statement: Set MyFriend = String1 + String2 results in: MyFriend = “yellow duckie”

Binary Machine Language – all data types consist of 1s and 0s 1 bit (0 or 1) 4 bits = nibble 1 byte = 8 bits = 2 nibbles Is the storage for one character 1 word = 4 bytes 1 K = 1 KB = 1 kilobyte = 1,0240 bytes = 210 bytes Kilo = 1,000 : 1 KB = 1,000 bytes 1 Meg = 1 megabyte (MB) = 1 million = 1024 KB 1 GB = 1 gigabyte (GB) = 1024 MB = 1,000,000,000 Many people approximate to steps of 1000, not 1024

Data Groupings: File Character: single symbol (letter, number, special symbol) “A”, “7”, “$” Field: group of characters forming a single data item “Smith” Record: a group of related fields Customer record containing name and address fields File: a group of related records Customer file, containing all customer records

Data Groupings: Database Character: single symbol (letter, number, special symbol) “A”, “7”, “$” Field: group of characters forming a single data item “Smith” Table: a group of related fields Customer record containing name and address fields Database: collection of related tables, that serve the information needs of the organization

Using Flowchart Symbols and Pseudocode Statements Flowchart: pictorial representation of the logic Pseudocode: English-like representation of the logic Example:

Flowchart input symbol:

Flowchart processing symbol

Flowchart output symbol:

Terminal symbol (start/stop symbol): Flowlines: Connect the steps Show the sequence of statements Have arrows to show the direction Terminal symbol (start/stop symbol): Shows the start and end points of the statements Lozenge shape

Flowchart vs. Psuedocode

Back-pointing arrows show statements that will be repeated

Infinite loop: a sequence of statements that repeats forever with no escape Avoid infinite loops by testing for a predetermined value that means “stop processing” Decision: testing a value Flowchart decision symbol: a diamond shape, with two flowlines, one for Yes and one for No

Sentinel value (or dummy value) Does not represent real data Signal to stop Can be used with input from files or from users End-of-file (EOF) marker: Code stored in the file that marks the end of the data Usually used instead of a sentinel value for file input

Flowchart connector symbol: Marks a logic transfer to another location in the flowchart Transfer location can be on the same page or on another page On-page symbol: a circle with a number or letter to identify the matching transfer location Off-page symbol: a square with a pointed bottom, containing page number and a number of letter to identify the matching transfer location

Assignment statement: Assigns a value to a variable Variable must appear on the left side, value on the right side of the assignment operator Right side may be an expression that will be evaluated before storing the value in the variable Assignment operator: the equal sign (=) in most languages Variable: Memory location: has an address and a value Value (contents) is used for various operations

Arithmetic Operations + Addition 2 + 3 = 5 - Subtraction 7 – 3 = 4 * Multiplication 5 * 4 = 20 / Division 12 / 3 = 4 ^ Exponentiation 2 ^ 3 = 8 % Modulus 14 % 3 = 2

Hierarchy of Operations 1st: perform operations inside parentheses (from inside out if more than one) 2nd: perform exponentiation 3rd: do multiplications, divisions, and modulus from left to right (if there are more than one) 4th: do additions and subtractions from left to right (if there are more than one)

Example of Hierarchy of Operations 3 * (6 + 2) / 12 – (7 – 5) ^ 2 * 3 = ? ( ) first: = 3 * 8 / 12 – 2 ^ 2 * 3 ^ next: = 3 * 8 / 12 – 4 * 3 Leftmost * next: = 24 / 12 – 4 * 3 Division next: = 2 – 4 * 3 Multiply next: = 2 – 12 Subtract last: = -10

Relational Operators Relational operators are the symbols used in the condition to be evaluated in If statements: = equal to <> not equal to < less than > greater than <= less than or equal to >= greater than or equal to

Comparison vs. Assignment Operators The equals sign (=) in this text may have two different meanings. The difference is very significant. As an assignment operator, the equals sign sets the value of an expression on the right side to the variable on the left side. As a comparison operator, the equals sign asks the question, “Is the value of the variable on the left side the same as the value of the expression, number, or variable on the right side?” Many programming languages distinguish between these two operators as follows: a single equals sign (=) signifies the assignment operator a double equals sign (==) signifies the comparison operator This is demonstrated in the examples that follow in the next slides.

Logical Operators Logical operators are used to connect simple conditions into a more complex condition called a compound condition. AND OR NOT

Hierarchy of Operations Type Operator Order Performed Arithmetic operations are performed first, in order shown ( ) ^ * / % + - 1st parentheses 2nd exponentiation 3rd: multiplication, division, modulus 4th: addition, subtraction Relational operations are performed second = <> < <= > >= All relational operators have equal precedence Logical operations are performed last, in the order shown NOT AND OR 1st: NOT 2nd: AND 3rd: OR

Two major programming techniques: Procedural programming Object-oriented programming Procedural programming: focuses on the procedures that programmers create Object-oriented programming: focuses on objects that represent real-world things and their attributes and behaviors Both techniques employ reusable program modules

Annotate the Output If the output consists of numbers or any data that has no explanatory text with it, you should annotate your output – this means to add some text so the user knows what the output means.