1. Bug Hunt Starter
• Use your developing
knowledge of VB to find
and correct the errors in
the example program.

2. Objectives
• Identify the scope of variables and distinguish
between local and global identifiers
• Identify and explain the use of constants and
variables in algorithms and programs.

3. Variables (general)
• A variable is a name used to refer to a particular
memory location that is used to store data
• Value can change while the program is running.
• Purpose if to allow the programmer to write code
that manipulates the data without knowing, yet,
what the data will be.

4. What data types that can be
applied to variables?
String Integer Byte
Long Double Decimal
Boolean Date/Time

5. Types of variables
• Declared at the beginning of the
code and is available throughout
Global the code, including all its
subroutines.
• Declared and used inside a
module or subroutine and is only
Local available in the module. Created
when subroutine is called and
destroyed when subroutine exits.

6. Program
Global Form 1
Local Sub Procedure
Local Sub Procedure
Local Sub Procedure
Local Sub Procedure

7. Program
Global (to form) Form 1 Global (to form) Form 2
Local Sub Procedure Local Sub Procedure
Local Sub Procedure Local Sub Procedure
Local Sub Procedure Local Sub Procedure
Local Sub Procedure Local Sub Procedure

8. Program
Global (to form) Form 1 Global (to form) Form 2 Global (all) Module
Local Sub Procedure Local Sub Procedure Local Function
Local Sub Procedure Local Sub Procedure Local Function
Local Sub Procedure Local Sub Procedure
Local Sub Procedure Local Sub Procedure

9. In action…

10. Variables top tips!
Use of spaces is not allowed. Use underscore or capitalisation
to make variables easier to spot. E.g. TimeOfArrival or
Time_of_Arrival
Give them sensible names, avoiding reserved words (IF, END,
OR, PRINT)
Use prefixes to help you remember data type e.g.
strFirstname, intAge
Select an appropriate data type – why?

11. Test yourself
1. What statement do you use to declare a local
variable in VB?
2. What statement do you use to declare a global
variable in VB?
3. What operator do you use to assign a value to a
variable?
4. In terms of security, why is a local variable better
than a global variable?
5. How should I create a variable that can we used
program wide and available to all forms?

12. Constants
• Used where values will not change
• Examples?
Declared as:
Const Public VAT as Decimal = 17.5
• Doesn’t require program to lookup value, always
known – time efficient.

13. In summary..
Global Variables: a variable declared at the
beginning of a program and accessible from
anywhere in the program
Local Variable: a variable declared in a program
block & accessible only within the program block
Constant: a value that does not change throughout
the program.