Welcome to TechRiz Where tech enthusiasts come for the latest tech news, Free downloads, free tutorials, articles and how to's. Description: This is the TechRiz Free Tutorials page. Visit every day to stay informed about the latest tech news, from security alerts to Hardware and software updates. Enjoy your stay. Week 3 – Visual Basic Tutorial Repetition Structures in Visual Basic A repetition structure allows the programmer to that an action is to be repeated until given condition is true. Do While... Loop Statement The Do While...Loop is used to execute statements until a certain condition is met. The following Do Loop counts from 1 to 100.
Dim number As Integer
A variable number is initialized to 1 and then the Do While Loop starts. First, the condition is tested; if condition is true, then the statements are executed. When it gets to the Loop it goes back to the Do and tests condition again. If condition is False on the first pass, the statements are never executed. While... Wend Statement A While...Wend statement behaves like Do While...Loop statement. The following While...Wend counts from 1 to 100
Dim number As Integer
Do...Loop While Statement The Do...Loop While statement first executes the statements and then test the condition after each execution. The following program block illustrates the structure:
Dim number As Long The programs executes the statements between Do and Loop While structure in any case. Then it determines whether the counter is less than 501. If so, the program again executes the statements between Do and Loop While else exits the Loop. Do Until...Loop Statement Unlike the Do While...Loop and While...Wend repetition structures, the Do Until... Loop structure tests a condition for falsity. Statements in the body of a Do Until...Loop are executed repeatedly as long as the loop-continuation test evaluates to False. An example for Do Until...Loop statement. The coding is typed inside the click event of the command button
Dim number As Long Numbers between 1 to 1000 will be displayed on the form as soon as you click on the command button. The For...Next Loop The For...Next Loop is another way to make loops in Visual Basic. For...Next repetition structure handles all the details of counter-controlled repetition. The following loop counts the numbers from 1 to 100:
Dim x As Integer In order to count the numbers from 1 yo 50 in steps of 2, the following loop can be used
For x = 1 To 50 Step 2
The following loop counts numbers as 1, 3, 5, 7..etc
For x = 1 To 50
To increase the space between the numbers increase the value inside the brackets after the & Space$. Following example is a For...Next repetition structure which is with the If condition used.
Dim number As Integer
In the output instead of number 4 you will get the "This is number 4". Exit For and Exit Do Statement A For...Next loop condition can be terminated by an Exit For statement. Consider the following statement block.
Dim x As Integer
The preceding code increments the value of x by 1 until it reaches the condition x = 5. The Exit For statement is executed and it terminates the For...Next loop. The Following statement block containing Do...While loop is terminated using Exit Do statement.
Dim x As Integer
With...End With statementWhen properties are set for objects or methods are called, a lot of coding is included that acts on the same object. It is easier to read the code by implementing the With...End With statement. Multiple properties can be set and multiple methods can be called by using the With...End With statement. The code is executed more quickly and efficiently as the object is evaluated only once. The concept can be clearly understood with following example. With Text1 In the above coding, the object Text1, which is a text box is evaluated only once instead of every associated property or method. This makes the coding simpler and efficient. VB Array - Arrays in Visual Basic 6An array is a consecutive group of memory locations that all have the same name and the same type. To refer to a particular location or element in the array, we specify the array name and the array element position number. The Individual elements of an array are identified using an index. Arrays have upper and lower bounds and the elements have to lie within those bounds. Each index number in an array is allocated individual memory space and therefore users must evade declaring arrays of larger size than required. We can declare an array of any of the basic data types including variant, user-defined types and object variables. The individual elements of an array are all of the same data type. Declaring arraysArrays occupy space in memory. The programmer specifies the array type and the number of elements required by the array so that the compiler may reserve the appropriate amount of memory. Arrays may be declared as Public (in a code module), module or local. Module arrays are declared in the general declarations using keyword Dim or Private. Local arrays are declared in a procedure using Dim or Static. Array must be declared explicitly with keyword "As". There are two types of arrays in Visual Basic namely: Fixed-size array : The size of array always remains the same-size doesn't change during the program execution. Dynamic array : The size of the array can be changed at the run time- size changes during the program execution. Fixed-sized ArraysWhen an upper bound is specified in the declaration, a Fixed-array is created. The upper limit should always be within the range of long data type. Declaring a fixed-array Dim numbers(5) As Integer In the above illustration, numbers is the name of the array, and the number 6 included in the parentheses is the upper limit of the array. The above declaration creates an array with 6 elements, with index numbers running from 0 to 5. If we want to specify the lower limit, then the parentheses should include both the lower and upper limit along with the To keyword. An example for this is given below. Dim numbers (1 To 6 ) As Integer In the above statement, an array of 10 elements is declared but with indexes running from 1 to 6. A public array can be declared using the keyword Public instead of Dim as shown below. Public numbers(5) As Integer Multidimensional ArraysArrays can have multiple dimensions. A common use of multidimensional arrays is to represent tables of values consisting of information arranged in rows and columns. To identify a particular table element, we must specify two indexes: The first (by convention) identifies the element's row and the second (by convention) identifies the element's column. Tables or arrays that require two indexes to identify a particular element are called two dimensional arrays. Note that multidimensional arrays can have more than two dimensions. Visual Basic supports at least 60 array dimensions, but most people will need to use more than two or three dimensional-arrays. The following statement declares a two-dimensional array 50 by 50 array within a procedure. Dim AvgMarks ( 50, 50) It is also possible to define the lower limits for one or both the dimensions as for fixed size arrays. An example for this is given here. Dim Marks ( 101 To 200, 1 To 100) An example for three dimensional-array with defined lower limits is given below. Dim Details( 101 To 200, 1 To 100, 1 To 100) Static and dynamic arraysBasically, you can create either static or dynamic arrays. Static arrays must include a fixed number of items, and this number must be known at compile time so that the compiler can set aside the necessary amount of memory. You create a static array using a Dim statement with a constant argument: 'This is a static
array. Visual Basic starts indexing the array with 0. Therefore, the preceding array actually holds 101 items. Most programs don't use static arrays because programmers rarely know at compile time how many items you need and also because static arrays can't be resized during execution. Both these issues are solved by dynamic arrays. You declare and create dynamic arrays in two distinct steps. In general, you declare the array to account for its visibility (for example, at the beginning of a module if you want to make it visible by all the procedures of the module) using a Dim command with an empty pair of brackets. Then you create the array when you actually need it, using a ReDim statement: 'An array defined in a BAS module (with Private
scope) If you're creating an array that's local to a procedure, you can do everything with a single ReDim statement: Sub PrintReport() If you don't specify the lower index of an array, Visual Basic assumes it to be 0, unless an Option Base 1 statement is placed at the beginning of the module. My suggestion is this: Never use an Option Base statement because it makes code reuse more difficult. (You can't cut and paste routines without worrying about the current Option Base.) If you want to explicitly use a lower index different from 0, use this syntax instead: ReDim Customers(1 To 1000) As String Dynamic arrays can be re-created at will, each time with a different number of items. When you re-create a dynamic array, its contents are reset to 0 (or to an empty string) and you lose the data it contains. If you want to resize an array without losing its contents, use the ReDim Preserve command: ReDim Preserve Customers(2000) As String When you're resizing an array, you can't change the number of its dimensions nor the type of the values it contains. Moreover, when you're using ReDim Preserve on a multidimensional array, you can resize only its last dimension: ReDim Cells(1 To 100, 10) As
Integer Finally, you can destroy an array using the Erase statement. If the array is dynamic, Visual Basic releases the memory allocated for its elements (and you can't read or write them any longer); if the array is static, its elements are set to 0 or to empty strings. You can use the LBound and UBound functions to retrieve the lower and upper indices. If the array has two or more dimensions, you need to pass a second argument to these functions to specify the dimension you need: Print LBound(Cells, 1) ' Displays 1,
lower index of 1st dimension Arrays within UDTsUDT structures can include both static and dynamic arrays. Here's a sample structure that contains both types: Type MyUDT The memory needed by a static array is allocated within the UDT structure; for example, the StaticArr array in the preceding code snippet takes exactly 400 bytes. Conversely, a dynamic array in a UDT takes only 4 bytes, which form a pointer to the memory area where the actual data is stored. Dynamic arrays are advantageous when each individual UDT variable might host a different number of array items. As with all dynamic arrays, if you don't dimension a dynamic array within a UDT before accessing its items, you get an error 9—"Subscript out of range." VB6 Arrays and variants (Visual Basic 6) Visual Basic lets you store arrays in Variant variables and then access the array items using the Variant variable as if it were an array: ReDim Names(100) As String, var As
Variant You can even create an array of Variant elements on the fly using the Array function and store it in a Variant variable: ' Arrays returned by the Array()
function are zero-based. Likewise, you can pass an array to a procedure that expects a Variant parameter and then access the elements of the array through that parameter: ' A polymorphic function that sums the
values in any array The most interesting feature of the preceding routine is that it works correctly with any type of numeric one-dimensional array. It even works with String arrays, but in that case you get the concatenation of all items, not their sum. This procedure is extremely powerful and reduces the amount of code you have to write to deal with different kinds of arrays. But you should be aware that accessing array items through a Variant parameter noticeably slows down the execution. If you need the best performance, write specific routines that process specific types of arrays. You can also pass a multidimensional array to a routine that expects a Variant parameter. In this case, you can still access the array elements through the Variants, but if you don't know at compile time how many dimensions the array has, your routine has to determine that number before proceeding. You can get this value using a trial-and-error approach: ' This routine returns the number of
dimensions of the array It's perfectly legal to use the function name inside a function's code as if it were a local variable, as the previous code snippet does. Often this technique lets you save a local variable and a final assignment before exiting the routine, which indirectly makes your code run slightly faster. Here's a modified ArraySum routine that uses NumberOfDims and works with both one- and two-dimensional arrays: Function ArraySum2(arr As Variant) As
Variant Often, if a Variant contains an array, you don't know the basic type of that array in advance. The VarType function returns the sum of the vbArray constant (decimal 8192), plus the VarType of the data included in the array. This lets you test that the array passed to a routine is of a given type: If VarType(arr) = (vbArray +
vbInteger) Then You can also test whether a Variant holds an array using the IsArray function. When a Variant variable holds an array, the TypeName function appends a pair of empty parentheses to its result: Print TypeName(arr) ' Displays "Integer()" As I've explained, you can either assign an array to a Variant variable or you can pass an array as a Variant parameter of a procedure. While the two operations look very similar, they're substantially different. To execute an assignment, Visual Basic makes a physical copy of the array. As a result, the Variant variable doesn't point to the original data but to the copy; from this point on, all the manipulations you do through the Variant variable don't affect the original array. Conversely, if you call a procedure and pass an array as a Variant parameter, no data is physically copied and the Variant simply works as an alias of the array. You can reorder array items or modify their values, and your changes are immediately reflected in the original array.
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