Visual Basic 'Net AAPP00832 VBN

1
Visual Basic .NetAAPP00-8-3-2 VBN
Functions Lecture 9
2
Topic Structure of the lesson

• function procedures
• exit sub and exit function
• generating (pseudo) random numbers

3
Learning Outcomes

• At the end of this lecture you should be able to
  
• Write a Function Procedure
• Use Exit Sub and Exit Function statements
• Generate random numbers

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 exams
• Function
• Exit
• RND

5
Functions

• A function is similar to a procedure in that it
  aids in modular design, i.e. breaking a problem
  down into smaller problems.
• Benefits of modular design
• isolate problems
• easier to develop and maintain code
• aids software re-useability

6
Different Modular Techniques

• Visual Basic has the following modular structures
• event procedures
• sub procedures
• functions
• The major difference between sub procedures and
  functions is that a function returns a value to
  the calling procedure.

7
Function Format

• Private Function FunctionName(var1 as type1,var2
  as type2,.) as datatype
• statement(s)
• FunctionName expression
• End Function
• Called by
• X FunctionName(arg1, arg2, )
• Parameters and arguments MUST AGREE in type and
  number.

parameter list
argument list
8
Example

• Option Explicit
• Private Sub cmdConvert_Click()
• Dim Fahrenheit as integer
• Fahrenheit InputBox(Temperature?)
• label1.caption FtoC(Fahrenheit)
• End Sub
• Private Function FtoC(fahr As integer) As double
• FtoC (5 / 9) (fahr - 32)
• End Function

9
Exercise 1

• Write a function to accept the radius of a circle
  from a textbox and display the area in a message
  box.
• Formula Area pi r r
• pi 3.142

10
Solution

• Option explicit
• Const PI 3.14159
• Private sub comand1_click()
• Dim radius, area as double
• radius CDbl(InputBox (Enter Radius))
• area areaofcircle(radius)
• MessageBox.Show (The area of a circle with
  radius
• radius is area)
• End sub
• Private function areaofcircle(rad as double) as
  double
• areaofcircle PI rad rad
• End Function

11
Exercise 2
Write a program to determine the volume of a
sphere using a function. Accept the radius from a
textbox. Display the volume on a label. Volume
of a sphere 4/3 pi r 3
12
Exit Function

• Executing Exit Function causes an immediate exit
  from the function
• Control is returned to the caller and the next
  statement in sequence after the call is executed

13
Exit Function Example

• Private sub cmddivide_click()
• Dim numerator , denominator as integer
• Dim result as string
• Numerator CInt(txtnum.text)
• Denominator CInt(txtden.text)
• Result divide(numerator, denominator)
• If result then
• MessageBox.Show ( Divide by Zero attempted)
• Else
• MessageBox.Show (result)
• End if
• End sub

14
Exit Function Example

• Private function divide(n as integer, d as
  integer) as string
• Dim answer as integer
• If d 0 then
• exit function
• Else
• answer n / d
• divide Integer division yields ans
• End if
• End Function

15
Random Number Generation

• the built-in VB function, RND, returns a random
  number in the range 0 lt random number lt 1
• To generate a random number between some other
  range Low High, use the following formula
• rand Low Int((High Low 1) Rnd)
• Example
• Dieface 1 Int(6 rnd()) to generate random
  numbers from 1 to 6

16
Exercise 3

• Write a program that will generate a random
  number from 5 to 100 when a command button is
  pressed.

17
Exercise 4

• Write a Function procedure that takes two
  String arguments representing a given name and
  family name, concatenates the two Strings to form
  a new String with the family name first followed
  by a comma and the given name last and returns
  the concatenated String.

18
Exercise 5

• Write a program that Inputs an Integer and
  passes it to function IsEven, which uses the
  Modulus operator to determine if the Integer is
  even.
• The Function should take an Integer argument and
  return True if the Integer is even and False
  otherwise.

19
Summary of Main Teaching Points

• Function Procedures
• are often used to solve an equation
• return a single value as the answer
• the arguments in the function invocation must
  match the parameter list of the function in both
  type and number

20
Next Session
Arrays
21
Question and Answer Session
Q A