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ITP 150

ITP 150. Week 4 Variables. Review:. BackStyle FillColor BorderStyle FillStyle Caption Name Enabled Visible. Controls Propeties Events Methods Procedures Functions. Move Clear SetFocus AddItem. Activate DragOver Load Change GotFocus LostFocus Click KeyDown MouseDown

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ITP 150

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  1. ITP 150 Week 4 Variables

  2. Review: BackStyle FillColor BorderStyle FillStyle Caption Name Enabled Visible • Controls • Propeties • Events • Methods • Procedures • Functions Move Clear SetFocus AddItem Activate DragOver Load Change GotFocus LostFocus Click KeyDown MouseDown DblClick KeyPress MouseMove DragDrop KeyUp MouseUp ITP 150 - Lecturer: A. Borquez

  3. Controls for Displaying andEntering Text To provide this featureUse this control Text that can be edited by the user, for example Text box an order entry field or a password box Text that is displayed only, for example to identify Label a field on a form or display instructions to the user ITP 150 - Lecturer: A. Borquez

  4. Controls That Present Choices to Users To provide this featureUse this control A small set of choices from which a user can choose one or Option buttons more options. Check boxes A small set of options from which (use frames if a user can choose just one. additional groups are needed) A scrollable list of choices from which the user can choose. List box A scrollable list of choices along with a text edit field. Combo box The user can either choose from the list or type a choice in the edit field.

  5. Controls That Display Pictures and Graphics To provide this feature Use this control A container for other controls. Picture box Printing or graphics methods. Picture box Displaying a picture. Image control or picture box Displaying a simple graphical element Shape or line control

  6. Managing Forms ITP 150 - Lecturer: A. Borquez

  7. Variables • In Visual Basic, you use variables to temporarily store values during the execution of an application • Variables have a name (the word you use to refer to the value the variable contains) and a data type (which determines the kind of data the variable can store) • To declare a variable is to tell the program about it in advance. You declare a variable with the Dim statement, supplying a name for the variable: Dimvariablename [Astype] ITP 150 - Lecturer: A. Borquez

  8. Variable rules…... • Must begin with a letter. • Can't contain an embedded period or embedded type-declaration character. • Must not exceed 255 characters. • Must be unique within the same scope, which is the range from which the variable can be referenced — a procedure, a form, and so on. ITP 150 - Lecturer: A. Borquez

  9. Visual Basic Variables • Variables: temporarily store values during the • execution of an application. Variables have a: • name (the word you use to refer to the value the • variable contains) and a • data type (which determines the kind of data the variable • can store). • Variables can be used in many ways, including: • ®As a counter that stores the number of times a procedure or code • block executes. • ®As a temporary storage for property values. • ®As a place to hold a value returned from a function. • ®As a place to store directory or file names. ITP 150 - Lecturer: A. Borquez

  10. Other Variable issues to think about…. • Implicit vs. Explicit Declarations • Declaring a variable in the Declarations section of a form, standard, or class module, rather than within a procedure, makes the variable available to all the procedures in the module. • Declaring a variable using the Public keyword makes it available throughout your application. • Declaring a local variable using the Static keyword preserves its value even when a procedure ends. ITP 150 - Lecturer: A. Borquez

  11. Variable Data Types Data typeStorage size Byte1 byte Boolean2 bytes Integer2 bytes Long (long integer)4 bytes Single (single floating-point)4 bytes Double(double floating-point) 8 bytes Currency (scaled integer)8 bytes Date8 bytes Object4 bytes + size of object String (variable-length)10 bytes + string length String (fixed-length)length of string Variant16 bytes ITP 150 - Lecturer: A. Borquez

  12. Variable Data Types Naming Conventions Data typePrefix Byte byt Boolean bln Integer int Long lng Single sng Double dbl Currency cur Date dtm Object obj String str Variant var ITP 150 - Lecturer: A. Borquez

  13. Understanding the Scope of Variables ScopePrivatePublic Procedure-level Variables are private to Not applicable. You the procedure in which cannot declare public they appear. variables within a procedure. Module-level Variables are private to Variables are available the module in which to all modules. they appear.

  14. Introduction to Procedures There are two major benefits of programming with procedures: • Procedures allow you to break your programs into discrete logical units, each of which you can debug more easily than an entire program without procedures. • Procedures used in one program can act as building blocks for other programs, usually with little or no modification. ITP 150 - Lecturer: A. Borquez

  15. Working with Date and Time • Dim dtNewDate As Date • dtNewDate = dtDate + 5 • Now, Date, and Time functions • MsgBox "The current date and time is " & Now() • MsgBox "The date is " & Date() • MsgBox "The time is " & Time() ITP 150 - Lecturer: A. Borquez

  16. VB Date/Time Functions FunctionExampleValue displayed Year()Year(Now)1999 Month()Month(Now)2 Day()Day(Now)22 Weekday()Weekday(Now)7 Hour()Hour(Now)11 Minute()Minute(Now)38 Second()Second(Now)9 ITP 150 - Lecturer: A. Borquez

  17. The DateDiff Function The DateDiff function returns the number of time intervals between two dates. • DateDiff(interval, date1, date2[, firstdayofweek[, firstweekofyear]]) • Dim dtTheDate As Date • Dim strMsg As String • dtTheDate = InputBox("Enter a date") • strMsg = "Days from today: " & DateDiff("d", Now, dtTheDate) • MsgBox strMsg

  18. VB Format Function the Format function accepts a numeric value and converts it to a string Format syntaxResult Format(Now, “m/d/yy”)1/27/99 Format(Now, “dddd, mmmm dd, yyyy”)Wednesday, January 27, 1999 Format(Now, “d-mmm”)27-Jan Format(Now, “mmmm-yy”)January-99 Format(Now, “hh:mm AM/PM”)07:18 AM Format(Now, “h:mm:ss a/p”)7:18:00 a Format(Now, “d-mmmm h:mm”)3-January 7:18 Using Named Formats • txtDate.Text = Format(Now, "Long Date") • txtCost.Text = Format(1000, "Currency")

  19. Sub Procedures vs. Function Procedures • Sub procedures do not return a value. • Function procedures return a value. ITP 150 - Lecturer: A. Borquez

  20. A Closer Look at Sub_Procedures... • A Sub procedure is a block of code that is executed in response to an event. • By breaking the code in a module into Sub procedures, it becomes much easier to find or modify the code in your application. [Private|Public][Static]Subprocedurename (arguments)statements • Each time the procedure is called, the statements between Sub and • End Sub are executed. • Sub procedures can be placed in standard modules, class modules, and form modules. • Sub procedures are by default Public in all modules ITP 150 - Lecturer: A. Borquez

  21. A Closer Look at Functions…. • Visual Basic includes built-in, or intrinsic functions, like Sqr, Val, or Chr. • You can use the Function statement to write your own Function procedures. [Private|Public][Static]Functionprocedurename (arguments) [Astype]statements • Like a Sub procedure, a Function procedure is a separate procedure that can take arguments, perform a series of statements, and change the value of its arguments. • Function procedures have data types, just as variables do. • You return a value by assigning it to the procedurename itself.

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