Visual basic datatype driver#

The following Visual Basic code takes a binary file and text file and uses the ADO stream object to store and retrieve data from an Oracle database using both Oracle's ODBC Driver and OLE DB Provider. Here's a technical note which could help you:

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Press F5 to run the program and clicking the button will produce the following message: Figure 9. MsgBox('Area of circle with ' & 'radius' & R & '=' & AreaCircle) 9.5 Declaring ConstantsР”В¬onstants are different from variables in the sense that their values do not change during the running of the program.The syntax to declare a constant in is Const Constant Name As Data Type = Value Example 9.4 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Public is the keyword that declares a global variable, which means it can be used by all the procedures and modules of the whole VB2019 program. Static keyword preserves the value of a variable even after the procedure is terminated. Most variables created inside a procedure are discarded by Visual Basic when the procedure is terminated. The Static keyword declares a variable that is being used multiple times, even after a procedure has been terminated. However, Private is rarely used, we normally use Dim to declare a local variable. Private declares a local variable or a variable that is local to a procedure or module. The above keywords indicate the scope of the declaration. The forms are as shown below: Private VariableName as Datatype Three other keywords are private, static and public. However, you can also use other keywords to declare the data. In Visual Basic 2019, we usually use the Dim keyword to declare the data. When you run the program, the following error messages will appear in a dialog box, as shown in Figure 9.3 Figure 9.3 For example, if you have declared a variable as an integer but you assigned a string value to it, an error occurred, as shown in Example 9.3: Example 9.3 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Total = firstNumber + secondNumber+ThirdNumberР”Р„nР’В error occurs when you try to assign a value to a variable of incompatible data type. The expression could be a mathematical expression, a number, a string, a Boolean value (true or false) and more, as illustrated in the following examples: firstNumber=100 The variable can be a declared variable or a control property value. *You may also declare a variable by assigning an initial value to it, as shown in the following examples: The syntax of an assignment in Visual Basic 2019 is Variable=Expression Running the program and clicking on the Calculate button produces the following output as shown in Figure 9.2.Р”Р„fter declaring various variables using the Dim statements, we can assign values to those variables. Private Sub BtnCal_Click(sender As Object, e As EventArgs) Handles BtnCal.Click We also use the Format function to display the current date of computation. There are three data types here, String, Integer and Date. In this example, we create a simple calculator where the user enter his name, two numbers and click the Calculate button to compute the addition of the two numbers. Running the code and clicking the show message button produces the following message: Figure 9.1 Example 9.2

Private Sub BtnShow_Click(sender As Object, e As EventArgs) Handles BtnShow.Click You can assign a value to the string using the = sign. Create a project and insert a Button and name ii as BtnShow and change its text to Show Message. This example declares two variables of the string type and concatenates them using the ampersand sign &. Or Dim VariableName1 As DataType1, VariableName2 As DataType2, VariableName3 As DataType3 Example 9.1

If you want to declare more variables, you can declare them in separate lines or you may also combine them in one line, separating each variable with a comma, as follows:

The syntax to declare a variable in VB 2019 is as follows: Dim VariableName As DataType