Basic data types
1.Numeric
|
Data type |
Size |
Value range |
|
Byte |
1 byte |
0 through 255 (unsigned). |
|
Double
(double-precision floating-point) |
8 bytes |
-1.79769313 486231570E+308 through
-4.9406 56458412 46544E-324 for negative values; 4.940656458 41246544E-324 through 1.797 693134862 31570E+308 for positive values. |
|
Integer |
4 bytes |
-2,147,483,648 through 2,147,483,647. |
|
Long
(long integer) |
8 bytes |
-9,223,372,036,854,775, 808 through 9,223, 372, 036,854,775,807. |
|
Currency |
8 bytes |
store monetary values. It supports 4 digits to the right of decimal point and 15 digits to the left |
|
Single
(single-precision floating-point) |
4 bytes |
-3.4028235E+38 through -1.401298E-45 for negative values; 1.40 1298E-45 through 3.4028235E+38 for positive values. |
2. String
Use to store alphanumeric values. A variable length string can store approximately 4 billion characters
3. Date
Use to store date and time values. A variable declared as date type can store both date and time values and it can store date values 01/01/0100 up to 12/31/9999
4. Boolean
Boolean data types hold either a true or false value. These are not stored as numeric values and cannot be used as such. Values are internally stored as -1 (True) and 0 (False) and any non-zero value is considered as true.
5. Variant
Stores any type of data and is the default Visual Basic data type. In Visual Basic if we declare a variable without any data type by default the data type is assigned as default.
User defined data types
Structure
In Visual Basic 6.0, you declare a structure using the Type ... End Type construction. The structure and its members all default to public access. Explicit access declaration is optional. The following example shows a valid structure declaration:
syntax :
Type tag declarators
[ Block ]
End Type
example :
Type Employee
EmpNumber As Integer
EmpOfficePhone As String
EmpHomePhone As String
End Type
Program execution control Statements
If...Then...Else Statements
An If...Then...Else statement is the basic conditional statement. If the expression in the If statement is True, the statements enclosed by the If block are executed. If the expression is False, each of the ElseIf expressions is evaluated.
syntax :
If Expression [ Then ] StatementTerminator
[ Block ]
[ ElseIfStatement+ ]
[ Block ]
[ ElseStatement ]
[ Block ]
End If StatementTerminator
example :
Dim iNumber As Integer
iNumber = Val(Text1.Text)
If iNumber < 5 Then
Text2.Text= "Number is Less than Five"
Else
Text2.Text= "Number is Greater than Five"
End If
Select Case
A Select Case statement executes statements based on the value of an expression.
syntax :
Select [ Case ] Expression StatementTerminator
[ CaseStatement+ ]
....
[ CaseElseStatement ]
End Select StatementTerminator
example :
Dim x As Integer
x = 10
Select Case x
Case 5
Text1.Text = "x = 5"
Case 10
Text1.Text = "x = 10"
Case 20
Text1.Text = "x = 20 ? 10"
Case 30
Text1.Text = "x = 30"
End Select
While Do While
A While or Do loop statement loops based on a Boolean expression. A While loop statement loops as long as the Boolean expression evaluates to True;
syntax :
1) While Expression StatementTerminator
[ Block ]
Wend StatementTerminator
2) Do [ WhileOrUntil Expression ] StatementTerminator [ Block ]
Loop [ WhileOrUntil Expression ] StatementTerminator
example :
Dim x As Integer
x = 3
Do While x > 0
Text1.Text = "Do While x > 0"
x = x - 1
Loop
x = 3
While x < 5
Text1.Text = "While x < 5"
x = x + 1
Wend
Do
Text1.Text = "While x = 2"
x= x+ 1
Loop While x > 2
For Loop
For/Next loops enable you to evaluate a sequence of statements multiple times.
syntax :
For [Expression]
[Block]
Next
example :
Dim x As Integer
For x = 1 To 10
Text1.Text = "VB In Easy Steps"
Next x