Vb lecture
- 1. Lecture 1 Visual programming using visualIDEs. Visual Basic is an IDE that allows you to develop Windows (Graphic User Interface - GUI) applications. The applications have a familiar appearance to the user. An integrated development environment (IDE) or interactive development environment is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools and a debugger. Most modern IDEs offer Intelligent code completion feature. Visual Basic has gone through many phases of development since the days of BASIC that was built for DOS . BASIC stands for Beginners' All-purpose Symbolic Instruction Code. The program code in Visual Basic resembles the English language. Different software companies had produced many different versions of BASIC for DOS, such as Microsoft QBASIC, QUICKBASIC, GWBASIC, and IBM BASICA and more. Then, Microsoft launched the first graphical BASIC which was known as Visual Basic Version1 in 1991. It is GUI based and especially developed for MS window. Since then the DOS versions of BASIC were slowly phased out and almost completely replaced by Visual Basic. Visual Basic was initially a functional or procedural programming language until the popular Visual Basic 6. Object-Oriented Programming language: Object-Oriented programming languages are event- driven. Here you don’t just have a series of statements that are executed, you have several choices of different things you can do in a program. You select the event that you want to occur. Only the code for that event is executed. Visual Basic is event-driven, meaning code remains idle until called upon to respond to some event (button pressing, menu selection, ...). Nothing happens until an event is detected. Once an event is detected, the code corresponding to that event (event procedure) is executed. Program control is then returned to the event processor. The final release was version 6 in 1998 (now known simply as Visual Basic). Though Visual Basic 6.0 IDE is unsupported as of April 8, 2008, the Visual Basic teamis committed to “It Just Works” compatibility for Visual Basic 6.0 applications on Windows Vista, Windows Server 2008 including R2, Windows 7, and Windows 8. Programming in VB is a combination of visually arranging components or controls on a form, specifying attributes and actions for those components, and writing additional lines of code for more functionality. Since VB defines default attributes and actions for the components, a programmer can develop a simple program without writing much code. Application (Project) is made up of: Forms - Windows that you create for user interface Controls - Graphical features drawn on forms to allow user interaction (text boxes, labels, scroll bars, command buttons, etc.) (Forms and Controls are objects.)
- 2. Properties - Every characteristic of a form or control is specified by a property. Example properties include names, captions, size, color, position, and contents. Visual Basic applies default properties. You can change properties at design time or run time. Methods - Built-in procedure that can be invoked to impart some action to a particular object. Event Procedures - Code related to some object. This is the code that is executed when a certain event occurs. General Procedures - Code not related to objects. This code must be invoked by the application. Modules - Collection of general procedures, variable declarations, and constant definitions used by application. Steps in Developing Application There are three primary steps involved in building a Visual Basic application: 1. Draw the user interface 2. Assign properties to controls 3. Attach code to controls Six windows appear when you start Visual Basic. 1. The Main Window consists of the title bar, menu bar, and toolbar. The title bar indicates the project name, the current Visual Basic operating mode, and the current form. The menu bar has drop-down menus from which you control the operation of the Visual Basic environment. The toolbar has buttons that provide shortcuts to some of the menu options. 2. The Form Window is central to developing Visual Basic applications. It is where you draw your application. 3. The Toolbox is the selection menu for controls used in your application. 4. The Properties Window is used to establish initial property values for objects. The drop- down box at the top of the window lists all objects in the current form. Two views are available: Alphabetic and Categorized. Under this box are the available properties for the currently selected object. 5. The Form Layout Window shows where (upon program execution) your form will be displayed relative to your monitor’s screen: 6. The Project Window displays a list of all forms and modules making up your application. You can also obtain a view of the Form or Code windows (window containing the actual Basic coding) from the Project window. Variables: Temporary memory location where we store data according to the datatype. Numeric (integer, double) String Boolean
- 3. Date Object Variant Variable types: Local: accessible only within a function or method or event procedure, where it is declared Form wide: accessible to all functions of a form where it is declared Application wide: accessible to all forms of an application in which it is declared Two ways of declaring variables: Implicit: automatically declare variant type Explicit: properly declare the variable and its type Dim a as integer (Dim: keyword) a=10 option explicit: we write option explicit to force our self to use explicit variables to minimize error chances. Example: Dim a as integer Input print Event procedure Event procedure a= inputbox(“Enter value of a”); print a