1 inf110 visual basic programming aubg spring semester 2011 reference books: schneider d., an...
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INF110Visual Basic Programming
AUBG Spring semester 2011
Reference books:Schneider D., An Introduction to Programming Using Visual Basic, Prentice Hall, Pearson Education Inc., 7th Ed. 2008, 6th Ed. 2006 Liberty J., Learning Visual Basic .NET, O’Reilly, 2002 Any Visual Basic book available in AUBG library
Course lecturer: Assoc. Prof. Svetla Boytcheva, PhD
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INF110 Visual Basic Programming AUBG Spring semester 2011
Lecture 11Title:
Visual Basic(Procedures2: Sub-s &
Function-s)
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Lecture Contents:
Reminder – basic ConceptsByVal parametersByRef parametersDemo programsPractical session
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ProceduresProcedures
Demo programs by Demo programs by J.Liberty,J.Liberty,
Chapter 06Chapter 06
06010601
INF110
Visual Basic Programming
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Reminder
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Basics of procedures:
“Properly designed functions permit to ignore how a job’s done. Knowing what is done is sufficient.”
B.Kernighan & D.Ritchie
“A function provides a convenient way to encapsulate some computation, which can then be used without worrying about its implementation. ”
B.Kernighan & D.Ritchie
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Devices for modularity
• VB.NET has two constructs for dividing problems into smaller pieces (sub-problems)
–Sub procedures
–Function procedures
They are blocks of code that can be referred to by a name.
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Sub Procedures and Function Procedures
- Two activities are must for effective processing with Sub Procedures and Function Procedures in VB:
- 1. Sub Procedures and Function Procedures are to be declared /defined, described/ in the source text of the program (it happens once only)
- 2. Sub Procedures and Function Procedures are to be called /activated, invoked/ (it may happen more than once)
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Sub Procedures
• General syntax to define/declare/describe
Sub ProcedureName()
block of code – VB statements
End Sub
• General syntax to call/activate/invokeCall ProcedureName()
Or justProcedureName() - Call is optional
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Module Module1
Sub Main()ShowMessage() ‘Sub invokedConsole.WriteLine(“Press Enter”)Console.ReadLine()
End Sub
Sub ShowMessage() ‘Sub definedConsole.WriteLine(“Greetings”)
End Sub
End Module
Note that user-defined procedures come after Sub Main()
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The power and versatility of a Sub may be increased by using parameters.
A parameter acts as “placeholder” for a value (of data) that you want to “pass” to the Sub.
Parameters are placed within the parentheses of the Sub declaration
Sub SubName()
Adding Parameters
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Module Module1
Sub Main()
ShowMessage(“Greetings”)ShowMessage(“Congratulations”)
Console.WriteLine(“Press Enter”)Console.ReadLine()
End Sub
Sub ShowMessage(Text As String)Console.WriteLine(Text)
End Sub
End Module
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Module Module1
Sub Main()ShowMessage(“Greetings”, 3)ShowMessage(“Congratulations”, 5)Console.WriteLine(“Press Enter”)Console.ReadLine()
End Sub
Sub ShowMessage(Text As String, Times as Integer)Dim Index As IntegerFor Index = 1 To Times
Console.WriteLine(Text)Next Index
End Sub
End Module
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Passing Data to Sub Procedure
• You can send items to a Sub procedure
Sum(2, 3)
Sub Sum(Num1 As Integer, Num2 As Integer)
• In the Sum Sub procedure, 2 will be stored in Num1 and 3 will be stored in Num2
• Num1 and Num2 are variables that are automatically available in the Sub procedure• Sum(10, 15)• Dim a As Integer = 40, b As Integer= 60• Sum(a, b)
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Parameter Passing by Value
• Keyword ByVal stands for “By Value”
• ByVal parameters retain their original value after Sub procedure terminates
Parameters must be declared using the format
ByVal Variable_Name As Data_Type
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Parameter Passing by Reference
• ByRef stands for “By Reference”
• ByRef parameters can be changed by the Sub procedure and retain the new value after the Sub procedure terminates
Parameters must be declared using the format
ByRef Variable_Name As Data_Type
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• Try to run and modify the ShowMessage()program in all the versions:
• with no parameters
• With one parameter
• With two parameters
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Functions
• Passes back a value to the calling procedure
• Calling
variable = funcname(arg1, arg2, etc)
• Function structure
Function funcname(param1 As type, param2 As type, etc) As type
statements
Return returnvalue
End Function
Returns a value
Return type
Note the assignment
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Functions
• Passes back a value to the calling procedure
• Calling
WriteLine(funcname(arg1, arg2, etc))
• Function structure
Function funcname(param1 As type, param2 As type, etc) As type
statements
Return returnvalue
End Function
Returns a value
Return type
No assignment, other context
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Example
Sub Main()Dim Item1 As Integer = 2Dim Item2 As Integer = 2Dim Sum As Integer
Sum = Add(Item1, Item2)‘Sum may be used as operand for processing‘Sum may be displayed using WriteLine()
End Sub
Function Add(Int1 As Integer, Int2 As Integer)As Integer
Return Int1 + Int2
End Function
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Exercise
• Try to run and modify the AddIntegers ()program in the following versions:
• With two parameters
• With three parameters
• With four parameters
• With five parameters
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Passing Arguments
ByVal
Sends a copy of the arguments value to a called procedure The called procedure cannot alter the original value of the arguments
ByRef
Send a reference indicating where the value is stored in memory The called procedure can alter the original value of the arguments
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Example 6-1
• Procedures as Unconditional Branching Statements– Branching to a method
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Example 6-1 Option Strict On Imports System Module Module1
Sub Main( ) Console.WriteLine("In Main! Calling SomeMethod( ) once...") SomeMethod( )
Console.WriteLine("In Main! Calling SomeMethod( ) twice...") Call SomeMethod( ) Console.WriteLine("Back in Main( ).") End Sub 'Main
Sub SomeMethod( ) Console.WriteLine(" Greetings from SomeMethod!") End Sub 'SomeMethod
End Module
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Example 6-1
Run the program.
Test the program.
Modify the program and rerun it again.
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More on unconditional branching
• Explicit statements to create unconditional branching:– Goto– Exit– Return– Throw
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Practical session 4
Procedures/Sub-s and Function-s/
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Practical task
Write a program that requests a number from 1 to 20, and then displays a row of that many asterisks using four loop constructs. Solution in three versions based on:
• VB program with Sub Main() only• User defined Sub procedure AstLine() with no
parameters• User defined Sub procedure AstLine(n) with one
parameter
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VB program with Sub Main() only
• Think your self or
• Look at the next slide
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VB program with Sub Main() onlyModule Module1
Sub Main() Dim I, n As Integer Console.WriteLine("Enter integer from 1 to 20") : n = Console.ReadLine()
Console.WriteLine() For I = 1 To n Console.Write("*") Next I
Console.WriteLine() : I = 1 While I <= n Console.Write("*") : I = I + 1 End While
Console.WriteLine() : I = 1 Do While I <= n Console.Write("*") : I = I + 1 Loop
Console.WriteLine() : I = 1 Do Console.Write("*") : I = I + 1 Loop Until I > n
Console.WriteLine() : Console.WriteLine()
End Sub
End Module
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User Sub AstLine() with no parameters
• Think your self or
• Look at the next slide
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User Sub AstLine() with no parametersModule Module1 Sub Main() AstLine() : Call AstLine() End Sub Sub AstLine() Dim I, n As Integer Console.WriteLine("Enter integer from 1 to 20") : n = Console.ReadLine()
Console.WriteLine() For I = 1 To n Console.Write("*") Next I
Console.WriteLine() : I = 1 While I <= n Console.Write("*") : I = I + 1 End While
Console.WriteLine() : I = 1 Do While I <= n Console.Write("*") : I = I + 1 Loop
Console.WriteLine() : I = 1 Do Console.Write("*") : I = I + 1 Loop Until I > n
Console.WriteLine() : Console.WriteLine()
End SubEnd Module
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User Sub AstLine(n) with one parameter
• Think your self or
• Look at the next slide
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User Sub AstLine(n) with one parameterModule Module1 Sub Main() Dim number As Integer Console.WriteLine("Enter integer from 1 to 20") : number = Console.ReadLine() AstLine(number) : Call AstLine(number) End Sub Sub AstLine(ByVal n As Integer) Dim I As Integer Console.WriteLine() For I = 1 To n Console.Write("*") Next I
Console.WriteLine() : I = 1 While I <= n Console.Write("*") : I = I + 1 End While
Console.WriteLine() : I = 1 Do While I <= n Console.Write("*") : I = I + 1 Loop
Console.WriteLine() : I = 1 Do Console.Write("*") : I = I + 1 Loop Until I > n
Console.WriteLine() : Console.WriteLine() End SubEnd Module
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Practical task
Write a program that requests a number for radius of a circle, and then displays the area of that circle. Solution in three versions based on:
• VB program with Sub Main() only• User defined Function Area() with no
parameters• User defined Function Area(n) with one
parameter
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VB program with Sub Main() only
• Think your self or
• Look at the next slide
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VB program with Sub Main() onlyModule Module1
Sub Main() Dim radius, res As Single
Console.WriteLine("Enter radius:") : radius = Console.ReadLine() res = 3.14 * radius * radius
Console.WriteLine("radius={0} area={1}", radius, res)Console.WriteLine("radius={0} area={1}", radius, 3.14 * radius * radius)
End SubEnd Module
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User Function Area() with no parameters
• Think your self or
• Look at the next slide
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User Function Area() with no parametersModule Module1
Sub Main() Dim res As Single
res = area() : Console.WriteLine("circle area={0}", res) Console.WriteLine("circle area={0}", area()) End Sub
Function area() As Single Dim r, result As Single Console.WriteLine("Enter radius:") : r = Console.ReadLine() result = 3.14 * r * r Return result
End FunctionEnd Module
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User Function Area(n) with one parameter
• Think your self or
• Look at the next slide
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User Function Area(n) with one parameter
Module Module1
Sub Main() Dim radius, res As Single Console.WriteLine("Enter radius:") : radius = Console.ReadLine() res = area(radius) : Console.WriteLine("radius={0} area={1}", radius, res) Console.WriteLine("radius={0} area={1}", radius, area(radius)) End Sub
Function area(ByVal r As Single) As Single Dim result As Single
result = 3.14 * r * r
area = result
End FunctionEnd Module
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User Function Area(n) with one parameter
Module Module1
Sub Main() Dim radius, res As Single Console.WriteLine("Enter radius:") : radius = Console.ReadLine() res = area(radius) : Console.WriteLine("radius={0} area={1}", radius, res) Console.WriteLine("radius={0} area={1}", radius, area(radius)) End Sub
Function area(ByVal r As Single) As Single Dim result As Single
result = 3.14 * r * r
Return result
End FunctionEnd Module
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User Function Area(n) with one parameter
Module Module1
Sub Main() Dim radius, res As Single Console.WriteLine("Enter radius:") : radius = Console.ReadLine() res = area(radius) : Console.WriteLine("radius={0} area={1}", radius,
res) Console.WriteLine("radius={0} area={1}", radius, area(radius)) End Sub
Function area(ByVal r As Single) As Single
return 3.14 * r * r
End Function
End Module
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User Function Area(n) with one parameter
Module Module1
Sub Main() Dim radius, res As Single Console.WriteLine("Enter radius:") : radius = Console.ReadLine() res = area(radius) : Console.WriteLine("radius={0} area={1}", radius, res) Console.WriteLine("radius={0} area={1}", radius, area(radius)) End Sub
Function area(ByVal r As Single) As Single
area = 3.14 * r * r
End FunctionEnd Module
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Practical task
Write a program that solves the Pythagorean Triple problem. Solution in three versions based on:
• VB program with Sub Main() only• User defined Sub procedure PythagorTriple1() with
two input ByVal parameters (m, n) and three output ByRef parameters (side1, side2, hypotenuse).
• User defined Function procedure PythagorTriple2() with one value returned by the function (hypotenuse), two input ByVal parameters (m, n), and two output ByRef parameters (side1, side2).
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Practical Task
Write a program that displays a n by m array (i.e. 10 rows by 10 columns) of asterisks. Solution in four versions based on:
• VB program with Sub Main() only• User defined Sub procedure Matrix()
with no parameters• User defined Sub procedure Matrix(n)
with one parameter • User defined Sub procedure Matrix(n,m) with two parameters
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Practical Task
Write a program that reads in 10 student test marks (percentages) and then displays the average mark, the lowest mark and the highest mark.
Use these marks: 87, 56, 73, 94, 89, 82,
85, 78, 43, 89. The list is terminated by –1
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Questions?Questions?
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Thank You For
Your Attention!