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Introducing Computer Science

Introducing Computer Science. CSCI N341: Client-Side Programming. Goals. By the end of this lecture you should … … understand Computer Science as the study of algorithms … recognize HIPO charts as one of several tools available for problem analysis

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Introducing Computer Science

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  1. Introducing Computer Science CSCI N341: Client-Side Programming

  2. Goals By the end of this lecture you should … … understand Computer Science as the study of algorithms … recognize HIPO charts as one of several tools available for problem analysis … understand how programming languages work in general … recognize different categories of programming languages … understand the program development cycle

  3. One Dimension of Web Programming Personal Computer - a computer operated by one person at a time, i.e. “Client” computer. N341 focuses on Client-Side computing Server – a computer whose resources and processors are shared by multiple users. N342 focuses on Server-Side programming

  4. What is Computer Science? • NOT about coding or hardware or software! • Computer Science is about PROBLEM SOLVING • Computer Science is about DEVELOPING ALGORITHMS to solve complex problems • Computers are merely tools for solving problems!

  5. Algorithms • Well-developed, organized approaches to solving complex problems • Test of a good algorithm: • Does the algorithm solve the stated problem? • Is the algorithm well-defined? • Does the algorithm produce an output? • Does the algorithm end in a reasonable length of time?

  6. Developing an Algorithm • Identify the Inputs • What data do I need? • How will I get the data? • In what format will the data be? • Identify the Processes: • How can I manipulate data to produce meaningful results? • Identify Outputs: • What outputs do I need to return to the user? • What format should the outputs take?

  7. Develop a HIPO chart – Hierarchy, Input, Processing, Output Developing an Algorithm

  8. Developing an Algorithm • Identify relevant modules • How can I break larger problems into smaller, more manageable pieces? • What inputs do the modules need? • What processes need to happen in the modules? • What outputs are produced by the modules?

  9. Programs • Sets of instructions that get the computer to do something • Instructions are translated, eventually, to machine language using an interpreter or a compiler (or both!). You can think of an interpreter as translating one “line” of code at a time, while a compiler translates an entire program before executing it • Programs may be a few lines or millions of lines of code

  10. Programming Tasks • All computer programs are written so they can take data, manipulate and then produce a result. • This process uses three distinct tasks: • INPUT – getting data from an external source (the user, a database, a file, etc.) • PROCESSING – actual manipulation of the data • OUTPUT – reporting the results of data manipulation back (using the monitor, writing information to a database, etc.)

  11. Categories of Languages • Machine Language • Binary digits (bits – 1s and 0s) which are translated to electrical impulses that get the computer to do something • “Native” language of computers • Assembly Languages • Group of basic commands, written as mnemonics, ie, jmp, hlt, etc. • Tied to specific processors • Still need to be translated to machine language

  12. Categories of Languages • High Level Languages • In terms of syntax, very close to human language (mostly English) • Lower error rate than writing machine language or assembly language programs • Need to be translated to machine language before execution • Compilers • Interpreters

  13. More on High-Level Languages • Features common to all HL languages: • Sequential Operations – Operations in which lines of code execute in order, one right after another • Control Structures • Conditional Operations – Operations in which execution depends on the outcome of a previous condition (usually evaluated to be TRUE or FALSE) • Looping Operations – Operations designed to repeat until a given condition is satisfied. • Branching Operations – Operations designed to identify mutually exclusive sections of code • Data Structures – allow programming optimization, ie, arrays, linked lists, etc.

  14. More Features • Variables – named storage locations for data • Data types – integers, strings, boolean, etc. • Delimiters – symbols that designate beginning and endings of programming structure, ie, “;”, “{“, etc. • Modularity – section of code that performs a task • Comments – Information for programmers for better code maintenance • Input and output – mechanisms for moving information in and out of a program • Key reserved words – words with predefined meaning within a language

  15. Levels of High-Level Languages • Procedural Languages • Early high level languages • Focus on structures • Examples include QuickBasic, Fortran, Pascal, Visual Basic (early versions) • Object-Oriented languages (OOP) • More recent development • Focus on data, not structures (Primacy of Data) • Examples include Java, C#, C++, Visual Basic.Net

  16. The Programming Development Cycle • Done after identifying inputs, processing & outputs • Steps • Analyze the problem using customer input and technical training • Plan a solution to the problem (algorithm) • Design the user interface • Prototype design to customer • Revise design based on customer feedback • Iterate and test to product release • Maintenance cycle • Product Obsolescence

  17. Notes on Development Cycle • 1. Analyze the Problem: Questions to ask: • Who is my intended audience? • What SPECIFIC outcomes does my audience expect? • What business rules do my audience expect to have incorporated into the solution? • What is the SCOPE of the problem?

  18. 2. Plan a Solution (Algorithm) • What types of programming structures are needed? • Sequential structures • Conditional structures • Looping structures • What data structures are needed? • Variables • Lists • Arrays

  19. 3. Design the User Interface • i.e. , The “UI” • Is the UI “learnable”? • Is it simple? (Limit user choices) • Does the UI promote error-proof use? • Is the layout of the UI arranged in a fashion conducive to the user’s culture and expectations?

  20. 4. Code the Solution • Develop an actual program from an algorithm • Should be the “easiest” part of the process – all the work should already be done!

  21. 5. Test & Debug the Solution • Alpha Testing – Internal testing done with expected client data (NOT LIVE DATA) • Beta Testing – Testing done at the client site with their data (USUALLY LIVE DATA) • Try to predict common user errors • Test subjects should be Power Users, Normal Users and Neophytes

  22. 6. Make Sure Documentation is Complete • User Documentation: • User Manual • Technical Documentation (for System Administrators) • Internal Documentation: • Documentation comments • Code comments • Procedural comments • Should be done while coding!

  23. 7. Plan Next Release • What bugs need to be fixed? • Are bugs “critical”? (Need to be fixed in a minor release) • If bugs are not critical, they can be fixed in next major release • What product enhancements do the users want for the next release?

  24. Internal Commenting • Comments are non-executable lines (the computer ignores them) which are used to communicate valuable information about code to others • Types of Internal Commenting: • Documentation Comments • Code Comments • Procedural Comments • Comment Syntax: • C-like Syntax (C, C++, Java, JavaScript): /* This will work for multi-line comments */ // This is a single-line comment

  25. Documentation Comments • Used to given specific information about a program • Usually found at the beginning of a code window • Include information about the author, creation date, purpose, modification date & modification history

  26. Documentation Comment /* • TITLE: Hello World, v2.0* AUTHOR: Susie Student* PURPOSE: To demonstrate changing of textbox properties using event procedures.* CREATED ON: 09.10.2002* LAST MODIFIED ON: 09.18.2002* LAST MODIFIED BY: RSM* MODIFICATION HISTORY:* 08.12.2009 - Renamed form to frmMain to conform with accepted naming standards (MJK) *11.18.2008 - Created a Clear Button enabling users to clear output (RSM) */

  27. Code Comments • “Tell the story” of the code, in English • For this class, you should use code comments to indicate what lines of code do • Define how variables are being used • Describe sections of code

  28. Code Comments /* Initialize loop counter to 1 */var counter = 1;/* Set loop to repeat 10 times */while(counter <= 10){ /* Display loop number*/alert(“You are on loop number” + counter); /* update counter*/counter++; } /* end while */

  29. Procedural Comments • Identify purpose, arguments & return values for procedures • Can be used in: • Event Procedures • Sub-Procedures • Function Procedures

  30. Procedural Comments /* Function touchRock Used to capture user name and produce custom greeting. If name is provided, upon image mouse click change image to happy rock */ Function touchRock(){ varuserName = prompt(“What is your name?”, “Enter your name here.”); if (userName) { alert(“It is good to meet you, “ + userName + “.”); document.getElementById(“rockImg”).src = “rock_happy.png”; } //end if } // end function touchRock

  31. Questions?

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