1. Sub Procedures and Functions
Visual Basic
Sub Procedures and Functions

2. Topic & Structure of the lesson
Introduction to Modular Design Concepts
Write Sub Procedures
Compare between Call by Value and Call by Reference

3. Write a sub program and pass arguments to it
Learning Outcomes
At the end of this lecture you should be able to :
Declare a sub program
Write a sub program and pass arguments to it
Write a Call-By-Value and Call By Reference sub procedure

4. Key Terms you must be able to use
If you have mastered this topic, you should be able to use the following
terms correctly in your assignments and tests:
Call
By Ref
By Val

5. Modular Design Concepts
Modularity refers to breaking a large problem down into smaller self-contained modules.
This allows the programmer to isolate problems within the program by looking at specific areas.
Without Breaking problems down into smaller modules will increase program maintenance cost.

6. Dividing code into procedures
Divide & Conquer Approach
Makes program development more manageable.
Software Reusability
Using existing procedures as building blocks for new programs
Avoid Duplicating programs

7. Different Modular Techniques
Visual Basic provides us with the ability to represent modules through the use of the following:-
Sub Procedures
Function Procedures
Event Procedures

8. Sub Procedures What are Sub Procedures?
Sub Procedures are subprograms or routines which are self contained and are used to perform a particular task.

9. Writing a Sub Procedure
Private Sub cmdAdd_click() Call add(2,1) End sub Private sub add(num1,num2 as integer) Dim total as integer total = num1 + num2 MsgBox total End Sub
Arguments
parameters

10. Quick Review Question
Write a program to accept two numbers using textboxes and pass the numbers into a subprogram called product to multiply them.
Display the answer in the product procedure.
Use a Msgbox to display the answer

11. Answer Private Sub cmdmultiply_Click() Dim a,b as integer
Call product (a, b)
End Sub
Private Sub product (num1 As integer, num2 As integer)
Msgbox ("The product of “ & num1 & "and“ & num2 & "is“ & num1 * num2)

12. No Arguments – No return value
MAIN PROGRAM
Private Sub Command1_Click( )
‘ Check the parenthesis. There is no argument
Call No_arg_No_return
End Sub
No arguments

13. No Arguments – No return value
SUB PROCEDURE
Public Sub No_arg_No_return()
Dim x, y, z As Integer
x = 20
y = 30
z = x * y
Label1.Caption = "TOTAL = " & z
End Sub

14. OUTPUT

15. Quick Review Question
Write a program that will accept three numbers and pass the numbers to a procedure minimum to determine the smallest number. Accept the three numbers using input box and display the smallest number on a text box.

16. Solution
Private Sub cmdSmallest_Click() Dim value1 As Long, value2 As Long, value3 As Long value1 = txtOne.Text value2 = txtTwo.Text value3 = txtThree.Text Call Minimum(value1, value2, value3) End Sub Private Sub Minimum(min As Long, y As Long, z As Long) If y < min Then min = y End If If z < min Then min = z lblSmallest.Caption = "Smallest value is " & min

17. Call By Reference
When you pass a variable to a sub procedure and return its updated value
By default Call By Reference is used in VB

18. Call By Reference - Procedure
Private sub a()
dim a as integer
a = 5
call square(a)
print a
end sub
private sub square(num as integer)
num = num * num
Ans a = 25

19. Call By Value
When you pass a variable to a sub program and it does not affect the value from the main program

20. Call By Value Private sub a() dim a as integer a = 5 call square(a)
print a
end sub
private sub square (byval num as integer)
num = num * num
Ans a = 5

21. Group Exercise
Write a program that accepts a student mark and passes the mark to a subprogram called grade which will determine the students grade.
Mark Grade A B C D
0 – 39 F

22. Follow Up Assignment
Write a program that uses a Sub procedure Maximum to determine the largest of three Integers. The smallest value is displayed in a Label.

23. String Functions The Len Function
The Len function returns an integer value which is the length of a phrase or a sentence, including the empty spaces. The syntax is
Len (Phrase)
For example,
Len (VisualBasic) = 11 and Len (welcome to VB tutorial) = 22
The Len function can also return the number of digits or memory locations of a number that is stored in the computer. For example,
X=sqr (16)
Y=1234
Z#=10#
Then Len(x)=1, Len(y)=4, and Len (z)=8

24. String Functions The Right Function
The Right function extracts a substring from a phrase, starting from the Right. The syntax is
Right (Phrase, n)
where n indicates the number of characters that you wish to extract starting from the right-most character.  For example,
 Right(“Visual Basic”, 4) = asic
The Left Function
The Left function extracts a substring from a phrase, starting from the left. The syntax is
Left(Phrase, n)
where n indicates the number of characters that you wish to extract starting from the left-most character..  For example,
 Left (“Visual Basic”, 4) = Visu

25. String Functions The Ltrim Function
The Ltrim function trims the empty spaces of the left portion of the phrase. The syntax is
Ltrim(Phrase)
.For example,
 Ltrim (“  Visual Basic”, 4)= Visual basic
Rtrim
Trim
Ucase and the Lcase

26. String Functions The Mid Function
The Mid function extracts a substring from the original phrase or string. The syntax is:
Mid(phrase, position, n)
Where position is the starting position of the phrase from which the extraction process will start and n is the number of characters to be extracted. For example,
Mid(“Visual Basic”, 3, 6) = ual Bas
The InStr function
The InStr function looks for a phrase that is embedded within the original phrase and returns the starting position of the embedded phrase. The syntax is
Instr (n, original phase, embedded phrase)
Where n is the position where the Instr function will begin to look for the embedded phrase. For example
Instr(1, “Visual Basic”,” Basic”)=8

27. String Functions The Rnd Function
Rnd is is very useful function for dealing with the concept of chance and probability. The Rnd function returns a random value between 0 and 1.
The Numeric Functions
The numeric functions are Int, Sqr, Abs, Exp, Fix, Round and Log.
a) Int is the function that converts a number into an integer by truncating its decimal part and the resulting integer is the largest integer that is smaller than the number. For example, Int(2.4)=2, Int(4.8)=4, Int(-4.6)= -5, Int(0.032)=0 and so on.
b) Sqr is the function that computes the square root of a number. For example, Sqr(4)=2, Sqr(9)=2 and etc.
c) Abs is the function that returns the absolute value of a number. So Abs(-8) = 8 and Abs(8)= 8.

28. Numeric Functions
d) Exp of a number x is the value of ex. For example, Exp(1)=e1 =
e) Fix and Int are the same if the number is a positive number as both truncate the decimal part of the number and return an integer. However, when the number is negative, it will return the smallest integer that is larger than the number. For example, Fix(-6.34)= -6 while Int(-6.34)=-7.
f) Round is the function that rounds up a number to a certain number of decimal places. The Format is Round (n, m) which means to round a number n to m decimal places. For example, Round (7.2567, 2) =7.26
g) Log is the function that returns the natural Logarithm of a number. For example,
Log 10=