Lesson 5: Managing Visual Basic 6 (VB6) Data

5.1 Understanding Visual Basic 6 Data Types

Data types in VB6 are essential for managing information effectively in applications. They are broadly categorized into numeric and non-numeric data types. This classification helps developers write efficient and accurate code.

5.1.1 Numeric Data Types in VB6

Numeric data types support mathematical operations. These include:

• Byte: Unsigned 8-bit number, 0 to 255.
• Integer: 16-bit signed integer, -32,768 to 32,767.
• Long: 32-bit signed integer, -2,147,483,648 to 2,147,483,648.
• Single: 32-bit floating-point, suitable for precision calculations.
• Double: 64-bit floating-point, supports larger precision and range.
• Currency: 64-bit fixed-point, ideal for financial values.
• Decimal: 96-bit, extremely precise, used for high-accuracy arithmetic.

5.1.2 Non-Numeric Data Types in VB6

These types do not support mathematical operations. Common examples include:

• String: Text values, can be fixed or variable length.
• Date: Stores date and time values between 100 AD and 9999 AD.
• Boolean: True/False values.
• Object: Holds object references.
• Variant: Can store any type of data and is flexible but less efficient.

5.1.3 Using Suffixes for Literals in VB6

Suffixes specify the data type of a literal value, allowing more accurate computations. Examples:

• & for Long
• ! for Single
• # for Double
• @ for Currency

Also, enclose string literals in quotes and date literals within # symbols.

Examples:

memberName = "Turban, John"
TelNumber = "1800-900-888-777"
LastDay = #12/31/2000#
ExpTime = #12:00 AM#
    

5.2 Working with Variables in VB6

Variables are placeholders for storing data in memory. You must name and declare them correctly for effective program design.

5.2.1 Naming Rules for Variables

• Must be less than 255 characters.
• No spaces or special characters like !, @, &, $.
• Must begin with a letter and cannot contain periods.

Examples:

Valid Names	Invalid Names
My_Car	My.Car
ThisYear	1NewBoy
Long_Name_Can_beUSE	He&HisFather

5.2.2 Declaring Variables Explicitly

Use Dim for local variables, and combine multiple declarations using commas. Example:

Dim name As String, age As Integer, score As Double
    

Fixed-length strings use:

Dim yourName As String * 10
    

5.2.3 Variable Scope in VB6

• Dim: Local scope
• Private: Module-level visibility
• Public: Global scope
• Static: Remembers values between procedure calls

5.3 Working with Constants

Constants hold values that do not change during program execution. Declared using the Const keyword.

Const Pi As Single = 3.142
    

Example: Calculate Area of a Circle

Uses a constant and several variables to compute the circle’s area based on user input.

Dim h, r, a, rad, area As Single
Const Pi As Single = 3.142

Private Sub CmdArea_Click()
  r = h / 2
  rad = r * 0.001763889
  a = Pi * rad ^ 2
  area = Round(a, 2)
  MsgBox ("The Area of the circle is " & area)
End Sub

Private Sub CmdResize_Click()
  h = InputBox("Enter the value of height")
  MyShape.Height = h
End Sub