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Constant Variable: Variables that do not change value during the execution of the program are called constants variables. Constant variables many times in your code. Declaring constants: The manner in which you declare constants is similar to the manner in which you declare variables. The syntax for declaring constant variables is as follows. The data type of constant variables is determined by the value you assign to it.

Constant can also have spoken. A constant variables declared with in a procedure can be access only by that procedure. Constant declared as public can be accessed by the entire application to declare public constants mention public infornt of constant word.

Constants declared in a module as public can be accessed by every procedure. Variable type conversations: In some situations you will need to convert variables from one type to another for this VB provides different data type conversation functions. Dim a as Integer. Individual variables can hold single value such as a number data or string. Arrays hold sets of data in array has a name as variable has and the value stored in array can be accessed by its index.

Suppose if you want to store sixteen salaries one for employee. You can declare 16 variables or you can declare an array with 16 elements. An array generally contains series of values which are distinguished by means of index. Declaring Arrays: Arrays must be declared with Dim statement followed by the name of array and the maximum number of values it can hold.

A 0 is the salary of first person; a 1 is the salary of second person and so on. Explicitly you can specify the type of the arrays elements using as key word. Example: Dim a 10 as integer Dim name 10 as string. All the elements now in an array have the same data type. When the data type is variant for array then elements of an array can contain different types of data.

The number that appears in the parenthesis after the array name is called index or upper bound of an array. For example: Dim salary 16 as integer In these 16 is the upper bound the lower bound starts from 0. The upper bound in 1 less than that mentioned in parenthesis in you can explicitly specify the lower limit of the array. Example: Dim salary 1 to 16 as integer. Multi Dimensions array:- Single dimensional array stores single dimensional data.

Multi dimensional arrays stores data with more than two dimensional arrays has two indices. In such case you can declare dynamic array. To create a dynamic array declare it as usual with dim statement but do not specify its dimensions.

Re dimension dynamic user account user is the user enter value which specifies the dimension. The re dimension statement can appear only in a procedure re dimensions statement can change the bounds of the arrays. But not the no. Forcing variable declaration:- VB does not enforce variable declaration.

But for clean coding it is always better to declare variables. This statement tells the compiler to check each variables whether it is declared or not before using it and issue an error message if you attempt to use a variable with out declaring it. If you omit the option explicit. Statement VB creator variables as needed by itself. Let us consider an example following statement converts Germany dollars to US dollars. Another reason of declaring variable in advances is to simplify debugging in large application.

To avoid this application must enforce variables declaration then the compiler complain the DM2 USD variable has not been declared. Procedures: Procedures are useful for implementing repeated tasks such as frequently used calculation. Suppose you are writing an application that at some point it converts centimeters to inches or calculates the smaller of two numbers. This task in repeated in several places. To repeat in several places a procedure can be writing the same code in several places.

The benefits if writing a procedure is it is easy to understand and easy to maintain and the code in clear procedures are of two types. A commands click event procedure is a sub routine which is called each time the button in clicked. The statements in the sub routine are executed and when the end sub in reached, the control returns to the calling functions. It is possible to exit from a sub routine in between using exit statements.

Sub routine does not report anything to the calling program. The statements making up a function are placed in a pour of functions and end functions. Because functions report a result to the calling program it must have a type. Sum in a function that returns tomorrow date by adding one day to the current date. Because functions report the result to the calling program, the sum function has a type a date. Arguments: Argument is a value you pass to the procedure and the procedure acts on it.

This is how the sub routine and functions communicate with the application. Key ASCII is an argument which conveys the information about the key pressed functions also accepts arguments and in many cases more than 1.

Ex: The function sum accepts two numbers and returns the total of that two numbers. When you call procedure, you must supply values for all the arguments specified in the procedures definition and in the same order. Call him 10, 15 You can also omit the call statement and call to the sub routine by its name and arguments with in parentheses.

Calling functions: Functions are called by name a list of arguments follows the name in parentheses. Argument passing mechanism: There are two mechanism used to pass arguments.

When passing arguments by value. The procedure sends only the copy of the argument. Even if the procedure changes the argument value. They are not permanently changed. The advantages of passing argument by value are only the program in which they are declared can change their value.

Now the value n1 and n2 are printed as 10 and This is because the arguments are passed by value. When the argument are passed by value the changes mode to the function argument a, b take effect only with in the function.

The value n1 and n2 are not changed permanently. Also returns some value. Function statement. End if. End if 3 Select case. End if: This structure tests the conditions specified and if it is true, executed the statements, specified after the condition. This is used mainly to test a single condition. End if: This statement executes one block of statement if the condition is true and another if the condition is false. The general syntax is as follows.

Another variation of If …. The conditions are evaluated from top to button if any one of them in true. The corresponding block statements are executed and if name of the conditions are satisfied the else block will be executed. In the above example the expression is day date.

The value of that expression is compared with each case value. Some case statements can be followed by multiple value which are separated by , commas. Looping statement is an important plant of any program. VB supports the following loop statements. Do end 3 For Loop: The Do Once the condition becomes false the loop in terminated. There are two variations of do The general syntax is Do Once the condition becomes false the statements after the loop will be executed. If the condition is initially false.

The statements will never execute. Example: The below Do Do end: The while Once if the condition is false the statements after while Do end will be execute. Control is written to the while statement again which evaluates the condition again this process is repeated until the condition becomes false.

The for……next loop uses counter variables that increases or decreases in value during each repition of the loop. The loop in executed until the counter variable reaches the end value. The counter variable increased by one changing the old value in the loops body will not have any effect to the end value.

Once the condition is false the statements after while end will be executed. It has the following syntax. The general syntax of input box function is: Inputbox is prompt , default , response , y pos , title The above arguments are described as follows: Prompt: If required a string expression this displays the massage us the dialogue box. Title: It is optional it also requires string expression this displays the title of the dialogue box. If committee the application name is displayed.

Defaults: It is optional. This is displayed in the text box as the default value. If no input is provided, it committed the text box is displayed as empty. Response: It is optional it requires numerical expression this specifies the width of the input box.

Y pos: It is also optional and requires numerical expression this specifies the light of the input box. Msgbox function : This displays a message in a dialogue box waits for the user to click a button and return an integer indicating which button the user has clicked. Msgbox prompt button title Prompt: It requires a string expression.

This displays a message in a dialogue box. Button: Button argument is a numeric expression which is optional. It is sum of value specifying the number type of buttons to display. The icon style to display. The below value shows the constants and its value for the button argument. Constant value Description VB o. VB ok cancel 1 displays ok and cancel button VB abort, retry, syntax 2 displays abort, retry and ignore button.

VB yes, no cancel 3 displays yes, no and cancel buttons VB yes, no 4 displays yes and no buttons VB retry cancel 5 displays retry and cancel button VB questions 36 displays warning query, icon VB exclamation 48 displays information message icon VB information 0 first button is defaults VB default button2 second button is default VB default button3 third button is default VB default button4 fourth button is default.

More than one option can be specified in the button argument using plus operator. Each is independent of another. Drive list box: Displays the names of the drive connected to your PC.

The basic property of this control in the drive to be selected in the control. Drive list box or Dir list box: Displays the folders and sub folders of the current drive selected the basic property of this control in the drive path property which sets the drive list box to displays folders and sub folders.

File list box: Displays the file box of current folder. The basic property of this control in path. This property sets file list control to display all the files of the selected folder. If you place all the three controls on a form you can see the names of all the drives in the drive list box. Selecting any of them displays the names of all folders under dir list box control.

By double clicking on any one of the folder its sub folders are displayed. Similarly the file list box control will display the names of all files in the current folders. To force the dir list box to display the folders of the selected in the drive list box you must make sure that each time the user another drive the path properly of the dir list box control must match will the drive property of the drive list box.

The following is the minimum code you must place in the drive list box controls change event. Private sub drive1. Similarly each time the current selection is the dir list box control changes view must set the files list box controls path property to path property dir list box control. Private sub dir path, End sub. In most cases you may want to limit the number of files displayed in the file list box to do their use the pattern matching property of file list control.

It is nice and converts to display the file matching string in a combo box control from which the user can select any one of them. Changes in combo box are reported to the application using click event.

Private sub combo1- click File1. Types of Files in VB Files are organized to facilitate storage and retrieval of data rapidly. Random access is used when you want to access an individual record as rapidly as possible. You can read one byte at a time, or you can read them in groups. Binary access is mostly used to read or write files that are not to be read by humans. For effective use of the application, it must: Inform the user of the tasks that are available and Give the user the means to specify the task that is to be performed An application must provide a convenient and consistent way to group commands and an easy way for users to access them.

It allows an application to present the user with a means of initiating different actions The Menu Bar : Appears immediately below the title bar on the Form , Contains one or more menu options. Using too many levels of menus can make the application confusing to the user, Two or three levels are mostly used to design Menus. Visual Basic uses the menu editor to design menus and Most of the control properties can be set using the Menu Editor Menu Control Properties: 1. Caption: Text that appears on the control 2.

Name :Used to reference the menu control from code, Visual Basic does not allow us to exit the editor unless we give each menu control a name 3. Checked: Sets a value that determines whether a check mark is displayed next to a menu item 4. When we type a menu item in the Caption text box, the same item also appears in the menu control list box, Selecting an existing menu control from the list box allows us to edit the properties for that control.

Menus contain a number of options, logically organized and easily accessible by the user. Toolbars supplement the menus by providing quick access to a number of frequently used options. Yet menus and the toolbars take up little space, they can be made contextual.

Menu Conventions 1 Keep Menu captions short and simple. On the Menu Bar use one word for a title. More than one word can be confusing, as there are no separators. Any deviation from the windows conventions will result in confusion. A list can extend below the bottom, but avoid this if you can. Try to break it up into child menus where possible. Again remember that too many submenus is a bad design policy.

Again, stick to windows conventions. It offers mouse shortcuts for frequently used functions. If you do not have it on your Toolbox, do the following. And Push the OK button and you well see some new controls on your Toolbox. Now double click on the Toolbar control. A long flat button will appear on the form below the Menu Bar.

With the Toolbar in focus click the right-mouse-button. Select properties from the pop-up menu. Buttons : In this option, you can insert the buttons, set the control keys for the buttons, provide the ToolTip text, etc. Observe that the Image parameter is grayed. Add the buttons that you want. Supply the caption, the key to access the button, etc. The Key that you give here will be the reference you will use when you want to send the toolbar events to menu items.

Picture : View the picture of the icons selected. Multiple document Interface: The MDI was designed to simplify the exchange of information among documents, all under the same roof. With a MDI application, you can maintain multiple windows, but not multiple copies of the application. Data exchange is easier when you can view and compare many documents simultaneously. The main form or MDI form is not duplicated, but it acts as a container for all the windows, and it is called the parent window.

A MDI application must have at least two forms, the parent form and one or more child forms. There can be many child forms, but only one parent form. He parent form may not contain controls. While the parent form is open in the design mode, though the icons in the toolbox are not disabled, but you cannot place any control on the form.

But you can place controls in child forms. To create a MDI application follow these steps: 1. Make this form child by setting its MDIChild property true. To denote that this is a child form set its caption to MDIChild. Double-click your picture control in the tool box. It will appear as toolbar to your MDI form. Place three command buttons on this toolbar and change their names and captions to newchild, cascade and tile respectively.

The MDI window will look as in the below. Enter the codes as shown in the below. Save and run the project. See how you can arrange the child windows in tiles or cascades.

You cannadd any number of child windows by clicking the newchild button. A typical tile arrangement of child windows is shown in the below and cascade arrangement of the child windows in the below. To create an MDI application 1. Create an MDI form. Note An application can have only one MDI form. If no code in these QueryUnload event procedures cancels the Unload event, then each child is unloaded, and finally the MDI form is unloaded.

Because the QueryUnload event is invoked before a form is unloaded, you can give the user the opportunity to save a form before unloading it.

Features of MDI Form? In order to display as many documents as the user wants, your application will have to replicate itself as many times. If this were possible, imagine the number of controls, and the code that would have to be loaded in memory. There must be a more practical and efficient way to solve this problem.

It is in the form of the Multiple Document Interface MDI 1 An MDI application allows the user to display multiple documents at the same time, with each document displayed in its own window. Documents or child windows are contained in a parent window, which provides a workspace for all the child windows in the application.

The user can start an application, minimize it and close it with a single control , need not close all the Forms. After all functions like adding, displaying, sorting records, etc. Common controls can be available with the MDI form and share by the other forms.

Building User Interface The principles of design that is applicable in most interactive systems. These underlying principles of interface design Consistency:- Visual Basic offers a host of controls, However, do not make the mistake of using all of them. A number of controls can be used to do the same job. For a particular task have to use the particular control only. Fonts :- The fonts are another area where the designer might run away with his imagination.

Simplicity :- Make sure that the interface you present to the user is simple and easy to use. The interface is the place where you show a concern for the user who is not as knowledgeable about computers as you are.

It must be based on the thought pattern of an Average user. Try and think how the target user will accomplish this job. Provide clues where required without making an overkill. Usability :- The user must be able to use your application with ease. The user is also concerned with the help ,hints and guidance he can get from the applications itself. Images :- A picture is worth a thousand words. Your understanding of the theme will depend upon your frame of mind at the time.

That is the problem of using images or icons to convey a message. Use only those pictures and icons in your program that are universally understood and accepted. What you understand may not be what the user does. Colors :- Use Simple colors. The user is going to be looking at the form that you have designed.

Do not have too many colors on your form. When viewed on a color display, some of the colors may disappear. Compile Time Errors 2. Runtime Errors 3. Logic Errors 1. Compile Time Errors: These Errors occurs while writing the code.

They usually occur when the syntax of any visual basic statement is invalid. These Errors are easy to locate and correct. VB checks the syntax of each line of code as you enter and informs you by means of highlighted text. They do not occur until you run your application. Logic Errors: Logical Errors occur when your application produces in correct results. These errors normally occur due to a mistake made by the programmers. Error Description Syntax Error Occurs when we enter an incorrect line of code such as a mistake in typing a keyword, a punctuation is missing or an incorrectly spelled variable.

For example, using an If statement without a matching End If results in a syntax error. Visual Basic notifies us of the syntax errors before we leave a line of code. Run-time Error Occurs when a command attempts to perform an action that is not valid.

For example, a run-time error occurs if we try to assign a string to a numeric variable. Error handlers execute only if a run-time error is encountered. Logic Errors Occurs when an application executes without syntax errors or run-time errors, but the results are not what we intend.

For example, an application might prompt the user for a password but then may not allow access to the application even if the password is correct. This might be acceptable during development and testing phases. So, your code should trap and deal with its own errors. This statement waits for an error to occur and when the error occurs the error trap statement performs an action written under error handler.

On error statement has three forms. On Error Goto Label 2. On Error Resumenext 3. On Error Goto 1. On Error Goto Label : using this statement in your code, makes VB application to jump to a specific location in your code, if an Error occurs. Errors handle code is always written at the end of the procedure. This is because in the code, If no error occurs, you must exit the procedure, before reaching the error handler. Otherwise VB executes Error Handling code. On Error Resume Next : It tells VB application to suppress the standard error message and simply execute the next line of code.

If the file exist the kill procedure deletes it. But, it is suppressed due to an error resume next statement and procedure terminates normally. This has a number of properties. The most important properties are number and description. Property Description Number Returns or sets a numeric value specifying an error. We use the Number property to determine which error occurred. The value of the property is a unique number that corresponds to the error condition.

Syntax: Object. Number Description Returns or sets an expression containing a descriptive string associated with an error. ActiveX Components. But some Objects in windows environment are not unique to Visual Basic and they do not come with visual basic language. So, other applications provide these Objects and use them with in you applications. OLE Enables to access the functionality of multiple applications, with in single programming environment.

OLE is not a programming technique but it is a technology provided only in windows environment. OLE Terminology: 1.

A Component is an Item a control or an application that some one else has developed. Compound Document: A document that contains more than a single type of Object is called a Compound Document.

Container Application : An application that contains Linked or Embedded Objects is an container application. Object Embedding: with this technique you can insert an Object from one application into another application.

Object Linking: This technique is similar to Object Embedding except that the changes made to the Object Word or Excel in the server are reflected automatically in the container application. By selecting the Object through insert Object dialog box.

Embedding with Drag and Drop : 1. Immediately insert dialog box appears chick on cancel button. Since we are Embedding Object using Drag and Drop. Start an application that supports OLE and open a file. In this exaple, we will start Microsoft Word application and insert a Word Document in the OLE container control by dragging and dropping the document Copy and paste. You can edit it with words Menus and Tool Bars. Linking and Embedding with insert Object Dialog Box: 1.

Immediately insert Object Dialog Box appears. From that Dialog Box select the option create from file option button and check the Check Box. Click on the browse button to locate the file you want to Embed. Immediately the selected file appears on the OLE container control. ActiveX : What is ActiveX? ActiveX is a reusable and portable software component or control built according to what are called COM Component Object Model specifications.

It is the brainchild of Microsoft. It provides a building block solution to complex problems. Visual Basic ActiveX Controls: When you start VB, the first window called the design window shows some 20 intrinsic controls like label, command button, option button etc.

These controls cannot be removed from the Toolbox. These controls can be added to or removed from the Toolbox. You will get the New Project Menu as shown in the figure 1. When you move the mouse pointer over the icon, the names of the controls will appear below them. The Components Dialog Box will appear on the screen as shown in the figure 3. Select the required control by clicking on the rectangular box at the beginning.

After selecting the required controls, click OK. The icons of the selected controls will now appear on the Tool box and you can use them just as you will use any other intrinsic ActiveX control. This is in addition to the intrinsic controls already introduced in earlier versions. The Common Dialog Control enables the users to create Dialog Boxes open, save, print, setup, font, help and so on in their own applications.

The Animation Control enables the users to play silent avi files producing animation appropriate to the operations performed. The Communication Control describes how to use it with a modem to dial a phone number, interact with another modem or add advanced communication functionality to your applications.

The ListView Control enables the users to organize and view the data in deifferent ways using the View Property. The MAPI Control enables the users to sign-on to an electronic messaging system, access an Inbox, send or receive messages or send file attachments. The Masked -Edit Control enables the users to create mask platforms that prompt them for date, time currency or customized data input.

The MSChart Control enables users to create barchrts, assign and edit backdrops and load data from an array. The Multimedia Control enables the users to control and manage t5he recording playback of a variety of multimedia using a simple push-button interface.

The ProgressBar Control enables the users to get a feedback about a lengthy operation by pictorially displaying a moving coloured bar. The Slider Control enables the users to select a range of data between a maximum and a minimum setting. The Sysinfo Control enables the users to determine the current operating system, how to monitor and respond to Plug and Play events or changes in AC and battery power status.

The Tabbed Dialog Control enables the users to present several dialogs or screens of information on a single form using the same interface. The TabStrip Control enables the users to create tabs by adding tab objects to the tab collection. Use an imagelist controlo to supply bitmaps for the tabs. This project requires a timer and two labels. The running time will be displayed in one label and the current date will be displayed in the other label. Drag one timer and two label controls into the form.

Give the labels appropriate size, font and border and set their caption property blank. Set the timer interval property as one second and the Enabled property as True. The project at the design time looks as in the below. Entering the Event Codes: Open the code window by double clicking the Timer control and enter the code as shown in the figure 4a. The clock will begin to run. The current date will be displayed in the other label.

The run mode window is as shown in the figure 5. Another important point you notice is that the timer control does not appear in the run mode, and is invisible, but works only from behind. RichTextBox Control allows the user to enter text with varying fonts and sizes. Set the command button caption and name as font. A font dialog box can be opened only through the Common Dialog control. The Common Dialog control box will be invisible during run time.

Save the form and the project. Enter the codes as shown in the below and finally save the project. ShowFont RichTextBox1. FontName RichTextBox1. FontSize RichTextBox1. FontBold RichTextBox1. FontItalic RichTextBox1. You type any text in the RichTextBox and select it. Click the font button. The font dialog box will open. Set the desired font and size. On deselecting the text, you will find the text printed in the desired font and size.

This includes a set of activities. These activities are 1. Preliminary Investigation 2. Determination of System Requirements 3. Design the System 4. Development of Software 5. System Testing 6. Implementation and Maintenance. Preliminary Investigation : This activity has 3 parts. Request Classification 2. Feasibility Study 3. So, the project request must be examined to determine what the organizer wants?

Feasibility Study: This activity determines whether the study requested is feasible or not. There are 3 aspects in feasibility study i Technical Feasibility : can the project be done with current equipment, available persons and with existing software.

Request Approval: Not all requested projects are feasible and desirable. So, the projects that are feasible and desirable must be put in to schedule. Determination of System of Requirements : Analysis working closely with Employees and Managers must answer these question to determine the system requirements.

What is being done? How is being done? How frequently does it occur? How well the task is being performed? To answer these questions systems analyst take to a verify of persons. Design to the System: The system design describes the data to be input, the data to be output and the procedures. This information is passed to programming staff.

So, that software development can begin, Designers are responsible for providing complete and clear information about the system to programmers. Development of Software: For the development of new system software developers install newly purchased software. System Testing: During system testing the system is used experimentally to test whether the system is according to the requirements.

In this activity input is given to the system and the results are examined. Implementation and Maintenance : Implementation is the process of checking the system have to be maintained that is modifications and changes will be made to the software to meet the new requirements. To draw such data flow diagrams, the different notations used are 1.

Process : This represents people procedures or devices that use or procedure data. Source or Destination : This may be people, programs or any other Entities. Data Store : The data store represents data bases each Component in Data Flow Diagram is labeled with a descriptive name. Data Flow Diagrams allows analysts to study how the data enter the process and how they are changed when they leave the process.

If the analyst want to review the overall system hw uses higher level Data Flow Diagrams. If they are instructed in studying one particular process they use lower level Data Flow Diagrams. Using Data Flow Diagrams users can make suggestions for modifications more accurately. Upgrading Microsoft Visual Basic 6. Free full VB. Download all 8 chapters or read them online. Get a focused, first look at the features and capabilities in Microsoft Visual Basic , Visual Studio , and the.

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