Overview History Hardware Software Software Development Life Cycle Programming Languages Structured Programming Defining the Problem cosc175 - lec1

History of computers First Generation computers (1951-1958) vacuum tubes used large amounts of electricity, heat,large and expensive 1946 - ENIAC - computed trajectories for U.S. Army 1951 - UNIVAC - first commercially available computer, census Second Generation computers (1959-1963) transistors, less heat more reliable, less expensive Third Generation computers (1964-1970) integrated circuits less heat, higher speed cosc175 - lec1

History of computers Fourth Generation computers (1971-present) microprocessor => Personal Computer Apple II (1977), IBM PC (1981) ARPANET (1969) WWW (1991) Today - cheaper, smaller, better Fifth Generation computers (present and beyond) Artificial Intelligence http://www.history.com/shows/modern-marvels/videos/who-invented-the-computer#who-invented-the-computer cosc175 - lec1

Computer Components (Hardware) Peripherals Central Processing Unit ( CPU ) Input Device Control Unit Arithmetic Logic Unit Output Device Auxiliary Storage Device Memory Unit ( RAM & Registers ) cosc175 - lec1

Software Systems Software Programming Environment Application Software Operating System – software that controls overall operation of computer DOS, Windows, Unix, Linux Programming Environment Editor/Compiler/Interpreter/Linker/ Debugger Application Software cosc175 - lec1

Software Development Life Cycle Define the Problem (Analysis) Design the Solution (Algorithm) Code Solution (Program) Test and Debug Maintain & Document cosc175 - lec1

SDLC cosc175 - lec1

1. Analysis What? Defining the Problem Requirements Generate and document a clear problem statement Need to talk to all stakeholders Most common cause of software system failure traced to poor requirements gathering IPO cosc175 - lec1

2. Design HOW? Planning Algorithm – expansion of steps in the IPO diagram Flowchart Pseudocode cosc175 - lec1

netPay = payRate * hrsWorked Start Input payRate Input hrsWorked netPay = payRate * hrsWorked Output netPay Stop Pseudocode: Input payRate Input hrsWorked netPay = payRate * hrsWorked Output netPay cosc175 - lec1

Design tools pseudocode flowchart Can be done easily on word processor Implements structured design elements well Not visual No standard Standardized visual Difficult to modify requires special software to do on computer cosc175 - lec1

An Algorithm is . . . Step-by-step procedures for solving a problem in a finite amount of time. We are learning to write algorithms and the computer is simply a fast and flexible tool for implementing algorithms. An algorithm is an ordered set of instructions such that:      (1) There are a finite number of steps.      (2) It takes a finite amount of time to execute the steps.      (3) Each step is precise in meaning, and “doable.”      (4) It solves a general class of problems. cosc175 - lec1

3. Code the Solution Choose language Edit – create source program Compile - translate Syntax error – violate rules of programming language Link Create an executable program cosc175 - lec1

4. Test and Debug Test with variety of data Debugging: locating and correcting errors Logic error or bug - flaw in algorithm Run-time error e.g. Divide by zero Programming packages usually have debugger software to help programmer cosc175 - lec1

5. Maintain and Document Maintenance – Changing and maintaining existing programs Most coding is actually maintenance Documentation – sometimes done by technical writers cosc175 - lec1

A Tempting Shortcut? DEBUG REVISE REVISE DEBUG DEBUG REVISE Shortcut? CODE GOAL TEST THINKING CODE cosc175 - lec1

Programming Languages Definition: languages with strict grammar rules, symbols, and words used to construct a computer program Machine Languages is not portable, runs only on specific type of computer is made up of binary-coded instructions (strings of 0s and 1s) is the language that can be directly used by the computer Assembly Language Mnemonic codes are used for the op. codes instead of binary, EXA: LDA N, SUB B assembly language program must be translated into machine language before it can be executed, ‘assembler’. High Level Languages portable similar to natural language Requires compiler – translates high-level language into machine code FORTRAN, Visual BASIC, COBOL, Pascal, Ada, C++, Java most are standardized by ISO/ANSI cosc175 - lec1

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Assembly Language cosc175 - lec1

C++ 1972 : C created by Dennis Ritchie at Bell Labs => 90% of UNIX is then written in C 1983: C++ - Bjarne Stroustrup at Bell Labs 1998 : ISO/ANSI standardization of C++ general-purpose programming language - many uses Flexible - few restrictions high demand for C,C++ programmers high level/low level Portable - leader in portability programmer oriented-"written by a professional programmer for professional programmers" cosc175 - lec1

1. Edit: write and type the program (source code) in C++ , Save as myProg.cpp 2: Compile: translate the source code into machine language => myprog.obj syntax error – violation of the rules of the language.  3: Link = bring in other code from libraries, bind the modules together, etc => myProg.exe 4: Run = run the executable file  Logic errors (bug) – An error caused by a mistake in programming instructions.A logic error causes a program to operate wrongly or produce incorrect data, but not to stop working cosc175 - lec1

Structured Programming Top-down Design– divide and conquer Modularity subprograms Stepwise refinement The Structure Theorem- Use 3 basic control structures to solve any problem Sequence Selection (if-then-else) Repetition (loop) cosc175 - lec1

SEQUENCE Display “Enter Name” Input name Display “Hello “ name cosc175 - lec1

SELECTION (branch) IF Condition THEN Statement1 ELSE Statement2 True . . . Statement2 False If (num > 0) Display “Positive” Else Display “Negative” cosc175 - lec1

LOOP (repetition) WHILE Condition DO Statement1 False . . . Condition True Statement cosc175 - lec1

SUBPROGRAM (function) . . . SUBPROGRAM1 SUBPROGRAM1 a meaningful collection of SEQUENCE, SELECTION, LOOP, SUBPROGRAM cosc175 - lec1

Computing Profession Ethics copy software only with permission from the copyright holder give credit to another programmer by name whenever using his/her code use computer resources only with permission guard the privacy of confidential data use software engineering principles to develop software free from errors cosc175 - lec1

As proposed by the project sponsor.                                                                        As proposed by the project sponsor. As specified in the project request. As designed by the senior analyst.                                                                        As produced by the programmers. As installed at the user's site. What the user wanted. cosc175 - lec1

Step 1:Analysis Define the Problem IPO 1. Input: Determine what is given =>nouns, adjectives 2. Output: Determine what is required 3. Processing: Determine the transformations needed,actions needed to produce the required output =>verbs, adverbs cosc175 - lec1

variables Input and output data Nouns Naming convention No spaces Meaningful names Usually begin with lowercase Examples: roomWidth, numPeople, studentName cosc175 - lec1

Example 1 Read three numbers, add them together and print the total. cosc175 - lec1

1. Identify inputs Underline nouns Read three numbers, add them together and print the total. Break up several values into separate variables cosc175 - lec1

1. Identify inputs fill Input column first Read three numbers, add them together and print the total. Break up several values into separate variables cosc175 - lec1

2. Identify outputs output column next Read three numbers, add them together and print the total. Break up several values into separate variables No verbs here cosc175 - lec1

3. Processing-Define processing steps by bolding verbs Read three numbers, add them together and print the total. cosc175 - lec1

Each verb is a process step Read three numbers, add them together and print the total. Hint: Usually follows: input, process, output cosc175 - lec1

Step 3: define list of actions Read three numbers, add them together and print the total. Hint: Use verbs these steps usually involve the input and output defined in step 1 cosc175 - lec1

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc175 - lec1

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc175 - lec1

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc175 - lec1