auto generate barcode vb net Fig. 7.1 in Visual Studio .NET

Making Quick Response Code in Visual Studio .NET Fig. 7.1

Fig. 7.1
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We now assign the following initial values to the form and control properties. Object Form1 Label1 Property Caption Caption Font Value Min of Two Numbers a = MS Sans Serif, 10-point
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PROCEDURES
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Object Label2 Label3 Text1 Text2 Command1 Command2
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Property Caption Font Caption Font Caption Font Caption Font Caption Font Caption Font
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Value b = MS Sans Serif, 10-point Determine the Smallest of Two Numbers MS Sans Serif, 12-point (none) MS Sans Serif, 10-point (none) MS Sans Serif, 10-point Go MS Sans Serif, 10-point
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These property assignments result in the form shown in Fig. 7.2.
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Fig. 7.2
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The required procedures (a sub procedure and two event procedures) are shown below.
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Sub Smallest(a, b) Dim Min If (a < b) Then Min = a MsgBox "a is smaller (a = " & Str(Min) & ")" ElseIf (a > b) Then Min = b MsgBox "b is smaller (b = " & Str(Min) & ")" Else Min = a MsgBox "Both values are equal (a, b = " & Str(Min) & ")" End If End Sub
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PROCEDURES
[CHAP. 7
Private Sub Command1_Click() Dim x As Variant, y As Variant x = Val(Text1.Text) y = Val(Text2.Text) Call Smallest(x, y) or: Smallest x, y End Sub Private Sub Command2_Click() End End Sub
The sub procedure (Smallest) is the same as that shown in Example 7.1. When the user clicks on the Go button, event procedure Command1_Click() is activated. This causes the two values entered in the text boxes to be converted to numerical values and assigned to the variants x and y, respectively. These values are then transferred to the sub procedure Smallest when the sub procedure is accessed via the Call statement. Within Smallest, the arguments (i.e., the values of x and y within the event procedure) are referred to as a and b. The sub procedure then determines which argument represents the smallest value and displays an appropriate message indicating the result. Fig. 7.3 shows what happens when the program is executed. Here the user has entered the values 5 and 3 for a and b, respectively. The message shown in Fig. 7.4 is generated when the user clicks on the Go button.
Fig. 7.3
Fig. 7.4
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PROCEDURES
When passing an argument by reference, the argument name may be preceded by the reserved word ByRef within the procedure definition; i.e.,
ByRef argument name As data type
The ByRef designation is not essential, however, because this is the default mode of transfer in Visual Basic. An argument passed by reference is usually written as a single variable within the calling statement. It may be possible, however, to write an argument as an expression within the calling statement and still pass its value to a procedure by reference (most programming languages do not allow expressions to be passed by reference). This works because the expression is assigned its own address, which is accessible from within the procedure. Note, however, that information cannot be transferred back to the calling portion of the program when the calling argument is written as an expression (see below). Arguments can also be passed to a procedure by value. In this case, the value assigned to each argument in the calling statement (rather than the argument s address) is passed directly to the corresponding argument within the procedure. This is strictly a one-way transfer; that is, the argument values are transferred from the calling statement to the procedure. If any of these values is altered within the procedure, the new value will not be transferred back to the calling statement. Passing arguments by value can be useful, however, since the arguments in the calling statement can always be written as expressions rather than single variables. In order to pass an argument by value, the argument name within the procedure must be preceded by the reserved word ByVal; i.e.,
ByVal argument name As data type
If a procedure includes multiple arguments, some may be passed by reference and others by value.
EXAMPLE 7.3 SMALLEST OF THREE NUMBERS
Let us now modify the program presented in Example 7.3 to find the smallest of three numbers by repeatedly using a variation of the sub procedure Smallest introduced earlier. Our strategy will be to enter three numbers, a, b and c, via text boxes, then call Smallest to determine the smaller of the first two values (a and b). This value (called min) will be returned to the calling portion of the program. Then Smallest will be called again, this time receiving the values for c and min, and returning the lesser of these. The returned value will again be called min, overwriting the previous value. This example further illustrates the manner in which information is passed back and forth between a calling program and a sub procedure. Each time the procedure is accessed, it will accept two numbers from the calling statement and return one (the smaller value) via a transfer by reference. The two input values can be transferred either by value or by reference; we will transfer by value, simply to illustrate the technique. The preliminary control layout is shown in Fig. 7.5. We now assign the following initial values to the form and control properties. Object Form1 Label1 Label2 Label3 Label4 Property Caption Caption Font Caption Font Caption Font Caption Font (Continues on next page) Value Min of Three Numbers a = MS Sans Serif, 10-point b = MS Sans Serif, 10-point c = MS Sans Serif, 10-point Min = MS Sans Serif, 10-point
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