What is Enumerated Data, User Defined Types, Expression, Operators and Comments?

Enumerated Data, User Defined Types, Expression, Operators and Comments.

Enumerated Data:

Enumerated Data is user define data, which is declared with word Enum, syntax for enumerated data is.

                                            Enum UserTypeName
                                                        Value 1
                                                        Value 2
                                                       ------------
                                                        Value n
                                            End Enum

The Value 1, Value 2, - , - , Value n are also called named constant. Each value of enumerated type data has a numbers are assigning to value implicitly or explicitly. This is shown in the following example.

Example:

             Start Visual Basic with a new Standard EXE project. Place two CommandButton Controls on a Form and write the following code in Click event of each CommandButton control and General Section of Form.

‘ In General Section      Enum listofitem1                Item1                ‘ implicitly assign 1                Item2                ‘ implicitly assign 2                Item3                ‘ implicitly assign 3         End Enum Enum listofitem2           Item11 = 30                ‘ Explicitly assign 30           Item21                        ‘ implicitly assign 31           Item23 = 12               ‘ Explicitly assign 12 End Enum

Private Sub Command1_Click ()      Dim item As Integer      Item = 2      Select Case item          Case 1, 2, 3                Print, “Item from listitem1”          Case 4, 5, 6                Print, “item not from listitem1”      End Select End Sub

Private Sub Command2_Click ()      Dim item As Integer      Item = 31      Select Case item          Case 12, 30, 31                Print, “Item from listitem2”          Case 48, 49                Print, “item not from listitem2”      End Select End Sub

Press F5 to run this project and press each CommandButton to check its output.

User Defines Types:

User's Defined data type is one which can be created by using type statement by a user. Syntax of Type statement is

  

                    [Private | Public] Type TypeName

                                 Variable are declared

                    End Type

When type statement is used in General Section of the Form then word Private  is used. Similarly Public word is used when type statement is used in a module section of the visual Basic. User defined data type is just like use of structures in C languages.

Example:

          Start Visual Basic with new Standard EXE Project. Place a CommandButton control on the Form and write following coding in the click event of the CommandButton and in General Section.

Private Type Student    Rano As Integer    Name As String End Sub

Private Sub Command1_Click ()      Dim x As Integer      x. Rno  = 10      x. Name = “ M Shahid “      Print “ Rno =   “; x. Rno ‘And Name =    “; x. Name   End Sub

Press F5 to run this project and press each CommandButton to check its output.

Expression:

An expression is the combination of operands ( variables/constants) and operators, which provides a result (+, _, >, 3, 5, 6 and etc). e.g.

• 5 + 3 - 3
• x > y and x > z

Operators:

Operators is a symbol or set of two symbols that performs an action between the nearest Operands in Visual Basic commonly following operators are used.

1. Arithmetic Operators
2. Relational Operators
3. Logical Operators

    1. Arithmetic Operators:

                          Arithmetic operators are used for calculation purposes. The list arithmetic operators and their description is shown in the following table.

Operator Symbol	Purpose/Description	Example
+	Addition	3 + 4 = 7
-	Subtraction	5 – 4 = 1
*	Multiplication	23 * 4 = 72
/	Division (Real)	2 / 3 = 1.666666666667
\	Division (Integer)	5 / 3 = 1
Mod	Remainder	5 Mod 3 = 2

    2. Relational Operators:

Relational Operators are used to form simple condition between different operands. The list of Relational operators and its description is shown in following table.

Operator Symbol	Purpose/Description	Example
>	Greater than	5 > 3
<	Less than	-5 < 90
>=	Greater than or Equal	X >= 5
<=	Less than or Equal	X <= y
=	Equal	w = s
<>	Not Equal	67 <> x

    3. Logical Operators:

Logical Operators are used to form a compound condition. Logical Operators are.

• And     ' The expression with And operator returns True value if both conditions on both sides of               And operator are True otherwise returns False.
• Or       ' The expression with or operator returns False value if both condition of Or operator are                 False otherwise return True value.
• Not     '  Used for negation purpose.

Comments ( or Remarks ):

Comments or remarks are those lines of the code of an application, which are not interpreted by the interpreter or compiler (i.e Ignored by interpreter/ compiler ). In Visual Basic a line of code can be a comment or remark if ( ' ) apostrophe symbol or the reserved word Rem is placed at the start, in the middle, or at any other place of the line. The portion after this ( ' ) symbol and word Rem shall not be executed by the interpreter or compiler e.g.

                        ' Line for Comment Or

                        Rem Line for comment

Both statements have same function.

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Posted in: Visual Basic