CIS II5- 6202 5 TEXTBOOK LECTURE 2

CIS II5- 6202 5 TEXTBOOK LECTURE 2 Hello Class, It was good to meet all of you in class and hope the materials presented is slowly but surely sinking in. With this I would like to summaries what we had discussed about in these threads, text, live lecture, online e-lecture. We covered a lot of information this week. We looked at Chapter 1, 2 and 3. In Chapter 1, we looked at the steps in program development. The main key is "Understand the problem", only when you understand the problem can you then find a solution. A question that is asked, how much time should I spend doing a program. Programming can become time consuming if you do not follow my suggestion. As the program become more elaborate use this rule. The basic rule is for you to spend at least 70% of your time on paper and then 30% on the computer. The more you put down on paper the less frustrating it gets in the long run. Some students take this advise and some don't, hence the frustration, the stress and you tend to spin your wheels and head nowhere. The steps I take are usually 1. IPO 2. Pseudocode/Flowchart 3. Visual Basic Using the same analogy, think about building a new house. The first thing you do is decide how many rooms you want, how big the house should be, and the basic layout of the floor plan – this is the analysis activity where you determine "what" needs to be done. Then, an architect takes the basic floor plan and creates a detailed design or blueprint of the house, which shows the exact measurements – this is the design, or "how" it will be done. Establishing what you need to do and then determining how you are going to do it must be correctly completed before you start building the house. This is as true for building a house as it is for building a software application, game, or website. So, before you learn how to do any programming, you need to learn how to analyze the requirements and create the logic and design that is used to construct the application. Just like when you build a house, you cannot build a program without a blueprint! (This blueprint is the Pseudocode). Remember what you will take with you to the next class (CIS170) is the Pseudocode and NOT the flowchart. Now let’s look at some definitions. An information system (abbreviated as “IS”) is a special type of system that collects data and transforms it into information that is usable by human beings. Data is a collection of numbers and characters that represents something. What it represents may not be obvious to a human being. The goal of the information system is to convert this data into a format the can be understood by a person. This understandable format is known as information. An information system performs three basic functions: 1. Input data into the system 2. Process the data to create meaningful information 3. Output the information for the user These three basic functions (often abbreviated as IPO) also appear in computer programs. An example, a basic layout of a Point-of-Sale (POS) system, which you often see at the checkout points in a store. These systems input stock identification numbers (often from bar codes), retrieve prices from a database, and produce a receipt for the customer. A program is a set of instructions that tells a computer how to perform a task. (A solution to a problem) The logic behind the program is known as an algorithm. Algorithms can be coded into computer programs using various programming languages, such as Visual Basic, C# (read “C Sharp”), C++, Java, etc. Algorithms are generally presented using either flowchart or pseudocode. A flowchart is a graphical representation of an algorithm. We used different symbols to identify different types of instructions. Pseudocode is an English-like language that can be used to present an algorithm as a list of instructions. You can see that there is a close tie between what is diagrammed in the flowchart and what is written in pseudocode. The flowchart symbols used are 1. Parallelogram for Inputs (whenever you want to input data to the computer) and Outputs (whenever you want to output data from the computer). 2. Rectangle for process (whenever the computer is going to perform an internal process that requires no user input, such as a calculation). 3. Lines show the flow (the arrowhead shows the direction of the flow of logic). So what are the advantages and disadvantages of Flowcharts vs Pseudocode Advantages of Flowcharts: you can “see” the flow of the logic Disadvantages of Flowcharts: Limited by the size of symbols and you must learn the proper symbols. Advantages of Pseudocode: No symbols to learn. Also allows you to write as little or as much detail as you like. Disadvantages of Pseudocode: You cannot see the flow of the logic easily. This week we looked at The Sequence Structure consists of a sequence of instructions that are executed one after the other. There is only one path to follow. (Start at the top and proceeds downwards) Assignment statements are used to perform calculation and store the result In Visual Logic, the assignment flowchart element is a rectangle with a variable on the left hand side (LHS) and an expression on the right hand side (RHS). When executed, the expression is evaluated, and the result is stored into the variable. Mathematical equations do NOT have the same meaning as in programming expression Eg. Answer = Number * 2 and Number * 2 = Answer (are the same as a Mathematical equation but not so in programming) The second is incorrect in programming. Variables, is the name given to a collection of temporary memory locations, designed to store a particular data item. Each variable has two components: its name (which does not change) and its value (which may change during execution). The values stored in constants cannot change. Variable and constant names should be unique and descriptive. All variable used in a program must be introduced. We do this with a Declare statement (done in Pseudocode but not in Visual Logic). Variables and constants have a name (called an identifier), a data type, and a scope. It is important that you have a good understanding of variables and the use of it in programming, For this class, your variables will conform to the following rules: • Variable names must be one word – The word may contain letters, numbers, hyphens or any other characters. – Variable name must start with a letter (eg. R2D2 is allowed) – NO SPACES!!! • Variable names must have some meaning – Meaningful names (x and y are not considered meaningful) – Use camelCasing notation • Example: (string variable) – robotName = “R2D2” – classStartDate = “8/28/2011” (numeric variable) – studentAge = 27 – grandTotal = 17.49 Data types identify what type of information is being stored in a variable and determine what operations can be performed on those values. The data types we will deal with in this class are characters, or alphanumeric or strings (“Visual Logic Dude”) integer or whole number (59) real or float or currency ( 3.14) boolean (true false) All programs have to be tested and debug. A bug is an error within your program. Testing is finding errors. Debugging is correcting those errors. Making errors is part of programming, what you will learn is how to find those errors. Visual logic has a debugger which is a tool that will help you find these errors. Three main classification of errors are Syntax error, Run-time error, and logic error. Note: the more errors you find the better your program will run. Objective is to have an error free program. Syntax error is the most obvious type of error. A syntax error will occur when the rules of the language are not followed. Syntax errors might be caused by errors in punctuation, format, or spelling. A logic error produces incorrect output. The program may still run, but the results are incorrect. The hardest one to debug is logic errors. An example of a logic error is when the question requires you to add two numbers but you decide to multiply the two numbers. This program produces incorrect results. Run-time errors occur when statements cannot execute correctly. An example of Run time error would be like dividing a number by zero or another example would be finding a square root of a negative number. Both of these are undefined. (impossible arithmetic operations) Most of you found the live lecture useful, remember you may watch it over and over again. For those of you who have NOT watched this, you might be at a lost. Read the book, watch the live lecture and DO the labs and ask questions. Look at the problems shown in the lecture area of ecollege for each week. Try doing these in Visual Logic. The more you practice the better you will understand this material Next week we will be getting into the different control structures that are available to programmers. One of these control structure is a decision making control structure, which we will get into more on week 3. If you do have any questions, please do not hesitate to email me at Happy programming. Take care Prof Naidu P.S. I have attach this same information in a word document if you are not able to see the picture In the not-too-distant past, computers were seen as devices that performed all sorts of tasks that were associated with mechanization. For example, a company that designed structural roof and floor systems would fill out information on a punch card and then feed it into a computer. The computer would spit out information about the types of forces the various parts of the structural member would endure. It was a laborious task. As technology became more advanced, the computer's role as a "task machine" changed. It is now a tool for problem solving. High-level language, because of its English-like syntax, makes the concept of programming more of an art, rather than a task. In your professional life, you will face challenges that will require problem-solving skills. These skills are part of a process in which one develops software. The software one designs becomes an integral part in an information system. The objective of this course is to teach you how to recognize the requirements needed to solve a problem and utilize the tools that follow the concept of programming logic. Programming logic is the basis on which particular programming languages are used. Using this logic, you will be able to develop a working solution in a real programming language. As you learn more programming languages, you will find that the basic concepts you are learning apply to all of them. The Software Development Process Back to Top Software development is simply a process that programmers and designers use to perform problem-solving techniques that aid them in developing a technical solution to a business problem. The business problem may be very simple or very complex. A simple business problem can be something such as the human resources department needing a report of all Level III managers. A complex business problem can be something such as a new product that will be sold over the Internet through the company website. It does not matter what the problem is; the steps to develop the solution are the same. Software development is completed through the following steps. 1. Understand the Problem In this first step, you will work with your client or customer to define and understand precisely what the problem is and why a solution is needed. You will ask many questions of your client or customer. You will then review the information you received with your client or customer. You need to ensure you answer the what, where, why, and when questions as thoroughly as possible during this review. Your client or customer needs to convey his or her information and knowledge to you so that you can continue to problem solve for a solution. You often have to be part detective and part counselor. You may need to help the client or customer understand that a solution may be expensive or may not be completely possible. The more information you gather to understand the problem, the more requirements you will have to move on to the next step. 2. Plan and Design the Logic Once you understand the problem, you will use the information gathered to plan the logic to your solution. During this planning, the design of your solution will take shape. Sometimes, during the planning process, you determine that you need more information. It is okay to go back to the first step in the process to gather more information in order to understand the problem. Usually, the planning involves a three-step process: identify the input, identify the processes, and identify the outputs. The input is what the program will receive while it executes or runs. The processes are the calculations. The outputs are the results sent to the customer or user of the program. 3. Develop the Logical Solution After you understand the problem and plan and design the logic, you are ready to develop the logical solution to the original problem. The logical solution is determined by using design tools, such as pseudocode and flowcharts, to develop documentation to be passed to the programmers for coding. Pseudocode designs are English-like statements that can easily be translated to actual programming code. Flowcharts are a visual representation of the flow or process of the solution. During the design, you will determine the data variables necessary to store the data and the step-by-step algorithm for the solution. This step is considered the artistic part of the software development process and is very rewarding! You will learn more about pseudocode and flowcharts later in this lecture. 4. Desk-Check the Design During this step, you will complete a desk -check of your logic. You will develop some sample test data to test your logic and ensure that the solution will work. You will look for logic mistakes (errors). Remember, your solution needs to produce the correct results. If your solution gives you the wrong answer, then your solution is not valid. Think of it this way: You deposited $50 into your checking account using your ATM. Your previous balance was $100. You expect your new checking account balance to be $150. Your deposit receipt says that your checking account balance is $50, not $150. You are not happy. The solution was incorrect. The program deducted the deposit amount instead of adding it to your balance. By completing a test with sample test data, you will be able to resolve many mistakes (errors) well before the customer or user sees it live. Complete a walkthrough of the logic. Often, the client or customer and the software developer meet and walk through the design. This can help determine any missing elements in the design from the perspective of the client or customer. The walkthrough can help determine whether the solution is on target with the needs of the client or customer. Anything missing can be identified up front and added prior to any actual programming being completed. 5. Translate the Design Into Code Translating the design into code is completing the program in the selected programming language (C#, C++, VB, etc.) which is human readable instructions that represent the program design. However, in order to execute on a computer, the human readable programming language code must be either compiled or interpreted into machine language in order for the computer to understand the program, and this compilation is part of the programming process. With compiled languages, the entire program is translated into machine language that is understood by the computer before it runs. With interpreted languages, each line of instruction is translated into machine language just prior to executing or running. 6. Deploy the Solution When everything is completed, the final step is to put your solution live. You will deploy, or put your solution into production. The customers will begin using your solution. How exciting is that? Your solution may now be used by thousands upon thousands of customers, maybe even across the world! 7. Documentation Although documentation is not considered a formal step in this process, it is still very important. The two types of documentation, internal and external, are useful when changes or troubleshooting are necessary. Examples of internal documentation would be comments after lines of code that explain what it does. External documentation can consist of hierarchy charts and desk-checking tools, in order to validate the program's requirements and make adjustments if necessary. One thing to note about program design is that there are different approaches to it, such as the following. • Procedure driven: The focus is on breaking down the processes into functions (small programs or modules) that perform specific tasks or return output contributing to the entire overall program. • Event driven: Event-driven programming is when an outside interaction triggers a certain response and causes the program to react accordingly. • Data driven: The data that are known about the program are the means by which the processes will act upon the data. The data are at rest until the processes will manipulate them. Analysis and Design Tools Back to Top Input-Process-Output Model (IPO) Once you understand the problem, you will learn how to build, or program, the design in your following programming courses. The following section will introduce you to a structured and repeatable method of analyzing and designing problems called the input-process-output (IPO) model of analysis and design. In order to be useful, our programs will input data, process the data, and output the results. We will then use this IPO program model as the foundation for our analysis and design. This model is one of the primary models used by professional programmers worldwide, and in this model, you will determine (1) the input, or what data come into the program; (2) the processes that transform the data; and (3) the output, or the information displayed to the user or provided to another computer system. Image Description As you begin your analysis of any new program, it is important that you use the IPO model to focus your attention on the smaller parts of the problem. You do this by concentrating on only the input to the program, and once you understand what the input is, you can concentrate on determining the processes necessary to transform the input into the output. Once you determine what the necessary processes are, you then concentrate on the desired output. The actual order that you perform the analysis in is not as important as ensuring that you concentrate on one thing at a time. For example, you can analyze the input first, then the processes, then the output, or it may make sense for you to determine the output first, then the input, and then the processes. The important thing to remember is not to try to do all three analysis steps at the same time! However, it is generally recommended that the process element be done last. Focus on one aspect of the problem description at a time, because this will reduce the complexity of the problem and give you a structured, repeatable method of analyzing and designing programs.