VDS-Chapter1-Understanding-Computer-System.pdf

PLF PROGRAM LOGIC FORMULATION chapter1 Understanding Computer Systems  Computer System ⦿ A computer system is a combination of all the components required to process and store data using a computer. - Hardware is the equipment, or the physical devices, associated with a comp...

PLF PROGRAM LOGIC FORMULATION chapter1 Understanding Computer Systems  Computer System ⦿ A computer system is a combination of all the components required to process and store data using a computer. - Hardware is the equipment, or the physical devices, associated with a computer. For example ( keyboards, mice, speakers, and printers are all hardware.) -Software is computer instructions that tell the hardware what to do. When you write software instructions, you are programming. 3  Software Types ⦿ Application software comprises all the programs you apply to a task, such as word processing programs, spreadsheets, payroll and inventory programs, and games. ⦿ System software comprises the programs that you use to manage your computer, including operating systems. 4 Operations in Computer Program ⦿ Input—Data items enter the computer system and are placed in memory, where they can be processed. Hardware devices that perform input operations include keyboards and mice. Data items include all the text, numbers, and other raw material entered into and processed by a computer. 5 Operations in Computer Program ⦿ Processing—Processing data items may involve organizing or sorting them, checking them for accuracy, or performing calculations with them. ⦿ Output—After data items have been processed, the resulting information usually is sent to a printer, monitor, or some other output device so people can view, interpret, and use the results. 6 Other Important Terms o Program code - The instructions you write using a programming language o Syntax - rules governing a programming word usage and punctuation. o Syntax errors - Mistakes in a language’s usage. o Random access memory, or RAM - is a form of internal, volatile memory. Programs that are currently running and data items that are currently being used are stored in RAM for quick access. 7 Other Important Terms o Compiler or interpreter - translate your source code into machine language o Machine language is also called binary language, and is represented as a series of 0s and 1s. 8 Two Truths and a Lie In each Two Truths and a Lie section, two of the numbered statements are true, and one is false. Identify the false statement and explain why it is false. 1. Hardware is the equipment, or the devices, associated with a computer. Software is computer instructions. 2. The grammar rules of a computer programming language are its syntax. 3. You write programs using machine language, and the compiler or interpreter converts the statements to a programming language. 9 Understanding Simple Program Logic Simple Program Logic o For a program to work properly, you must develop correct logic; 11 Simple Program Logic o Computer program to double any number you provide represented in English-like statements: input myNumber set myAnswer = myNumber * 2 output myAnswer 12 Simple Program Logic o The number-doubling process includes three instructions: o The instruction to input myNumber is an example of an input operation. A variable is a named memory location whose value can vary o The instruction set myAnswer = myNumber * 2 is an example of a processing operation. o In the number-doubling program, the output myAnswer instruction is an example of an output operation. input myNumber set myAnswer = myNumber * 2 output myAnswer 13 Understanding the Program Development Cycle Program development cycle 1. Understand the problem. 2. Plan the logic. 3. Code the program. 4. Use software (a compiler or interpreter) to translate the program into machine language. 5. Test the program. 6. Put the program into production. 7. Maintain the program. 15  Understanding the Problem ⦿ Professional computer programmers write programs to satisfy the needs of others, called users or end users. ⦿ Documentation consists of all the supporting paperwork for a program; it might include items such as original requests for the program from users, sample output, and descriptions of the data items available for input. 16 Planning the Logic ⦿ The heart of the programming process lies in planning the program’s logic. During this phase of the process, the programmer plans the steps of the program, deciding what steps to include and how to order them. ⦿ Algorithm is the sequence of steps or rules you follow to solve a problem. ⦿ Desk-checking is the process of walking through a program’s logic on paper before you actually write the program. 17 Coding the Program ⦿ After the logic is developed, only then can the programmer write the source code for a program. ⦿ Coding refers to the part of programming that deals with writing codes that a machine can understand. 18 QUESTION Which step is harder? Planning the logic or coding the program? 19 Using Software to Translate the Program into Machine Language ⦿ Languages like Java or Visual Basic are available for programmers ⦿ Someone has written a translator program (a compiler or interpreter) that changes the programmer’s English-like high-level programming language into the low-level machine language that the computer understands. 20 Testing the Program ⦿A program that is free of syntax errors is not necessarily free of logical errors. ⦿ A logical error results when you use a syntactically correct statement but use the wrong one for the current context. Example: Example: input myNumber input myNumber set myAnswer = myNumber * 2 set myAnswer = myNumber * 20 output myAnswer output myAnswer 21 Testing the Program ⦿ Debugging - The process of finding and correcting program errors Example: input myNumber set myAnswer = myNumber + 2 output myAnswer 22 Putting the Program into Production ⦿ Putting the program into production might mean simply running the program once, if it was written to satisfy a user’s request for a special list. ⦿ Conversion, the entire set of actions an organization must take to switch over to using a new program or set of programs. ⦿ Maintenance - after programs are put into production, making necessary changes is referred to as maintenance. 23 Two Truths and a Lie In each Two Truths and a Lie section, two of the numbered statements are true, and one is false. Identify the false statement and explain why it is false. 1. A program with syntax errors can execute but might produce incorrect results. 2. Although the syntax of programming languages differs, the same program logic can be expressed in different languages. 3. Most simple computer programs include steps that perform input, processing, and output. 24 Thank you for listening & have a nice day. Declaring and Using Variables and Constants  Data Types ⦿ Numeric - one that can hold digits and have mathematical operations performed on it. ⦿ String - can hold text, such as letters of the alphabet, and other special characters, such as punctuation marks. 27  Data Types Languages such as C++, C#, Visual Basic, and Java distinguish between integer (whole number) numeric variables and floating-point (fractional) numeric variables that contain a decimal point. Type-safety - feature of some programming languages that prevents assigning values of an incorrect data type. 28  Data Types ⦿ Numeric Constant - A specific numeric value. ⦿ String Constant - A specific text value, or string of characters, such as “Amanda”. String values are also called alphanumeric values. 29  Working with Variables ⦿ Variables are named memory locations whose contents can vary or differ over time. Example: input myNumber set myAnswer = myNumber * 2 output myAnswer A variable is a space in the computer memory that can contain a changeable piece of data. The term “variable” comes from the Latin word “variabilis” which means “changeable”. 30  Working with Variables ⦿ A declaration is a statement that provides a data type and an identifier for a variable. ⦿ An identifier is a program component’s name. The identifier is the “name” of the variable. 31  Working with Variables ⦿ A data item’s data type is a classification that describes the following: - What values can be held by the item - How the item is stored in computer memory - What operations can be performed on the item 32  Working with Variables ⦿ Initializing the variable - Declaring a starting value to a variable Example: num mySalary num yourSalary = 14.55 string myName string yourName = "Juanita" ⦿A variable’s unknown value commonly is called garbage. 33  Naming Variables ⦿ As a programmer, you choose reasonable and descriptive names for your variables. ⦿ The language translator (interpreter or compiler) then associates the names you choose with specific memory addresses. ⦿ Keywords are not allowed as variable names because they are part of the language’s syntax. Example : num and string 34 Variable Naming Conventions 35 Variable Naming Conventions 36 37  Rules in Naming Variables 1. Variable names must be one word. 2. Variable names must start with a letter. 3. Variable names should have some appropriate meaning. 38  Assigning Values to Variables ⦿ Assignment statement - this statement incorporates two actions that uses = symbol as an assignment operator. Example: set myAnswer= myNumber * 2 39  Assigning Values to Variables The assignment operator is an example of a binary operator, meaning it requires two operands— one on each side. (An operand is simply a value used by an operator.) The assignment operator always operates from right to left, which means that it has right- associativity or right-to-left associativity. 40  Assigning Values to Variables ⦿ Valid Assignment Statements Example: set someNumber = 2 set someNumber = 3 + 7 set someOtherNumber = someNumber set someOtherNumber = someNumber * 5 41 Assigning Values to Variables ⦿ lvalue - The result to the left of an assignment operator. The l is for left. Example: Not valid set 2 + 4 = someNumber set someOtherNumber * 10 = someNumber set someNumber + someOtherNumber = 10 42 Assigning Values to Variables ⦿ Assignment Statements in Simpler Form Example : someNumber = 2 someOtherNumber = someNumber 43 Assigning Values to Variables ⦿ Assignment Statements Example : valid Example : Invalid taxRate = 2.5 taxRate = "2.5" inventoryItem = "monitor" inventoryItem = 2.5 taxRate = inventoryItem inventoryItem = taxRate 44  Declaring Named Constants ⦿ Named constant - similar to a variable, except it can be assigned a value only once. Example : num SALES_TAX_RATE = 0.06 Example : taxAmount = price * 0.06 taxAmount = price * SALES_TAX_RATE 45 Thank you for listening & have a nice day. 46