Functions and Subroutines in Visual Basic

Functions and Procedures

• Functions and Procedures (1.6)

  • Functions and subroutines are types of program units used to divide a program into smaller, more manageable parts.

  • Subroutines (Procedures): مجموعة من التعليمات تنفذ مهمة محددة ويمكن استدعاؤها أكثر من مرة من أجزاء مختلفة من البرنامج.

  • Functions (الدوال): تشبه الإجراءات الفرعية ولكنها تُرجع قيمة واحدة كنتيجة لتنفيذها.

• Subroutines (البرامج الفرعية)

  • تُستخدم لتنفيذ مهام محددة ويمكن استدعاؤها عدة مرات.

  • يمكن أن تستقبل معاملات (مدخلات) لتخصيص سلوكها.

  • لا تُرجع قيمة بشكل مباشر، ولكن يمكنها تعديل قيم المعاملات المُمررة إليها.

• Functions (الدوال)

  • تُستخدم لتنفيذ عمليات حسابية أو منطقية وإرجاع قيمة واحدة.

  • تستقبل معاملات (مدخلات) لتحديد البيانات التي ستعمل عليها.

  • يجب أن تحتوي على جملة إرجاع تحدد القيمة التي ستُرجعها الدالة.

• Functions return a value, subroutines do not.

• Subroutines perform an action, functions calculate a value.

• Subroutines may or may not have arguments, functions usually have arguments.

Subroutines

• Definition: A block of code that performs a specific task.

• Declaration: Starts with Private Sub followed by the subroutine name and parameters, and ends with End Sub.

  • Example:

    Private Sub sub_add_numbers(x As Integer, y As Integer)
    ' Code to add numbers
    End Sub
    

• Placement: Subroutines can be placed in:

  • Form (General section): Accessible from any control on the form (Private Sub).

  • Module: Accessible from any form or control in the project (Public Sub).

    • To add a module, select "Add Module" from the "Project" menu.

• Parameters: Variables that represent input or output values.

  • Input Parameters: Values passed into the subroutine.

  • Output Parameters: Values returned or modified by the subroutine.

• Calling a Subroutine: Use the Call statement or simply write the subroutine name.

  • Syntax:

    Call sub_name(Par1, Par2, ..., Parn)
    

    Or

    sub_name(Par1, Par2, ..., Parn)
    

• Event-Driven Subroutines: Execute when a specific event occurs (e.g., button click).

  • Example:

    Private Sub Command1_Click()
    ' Code to execute on button click
    End Sub
    

    • Command1_Click is a subroutine that runs when Command1 is clicked.

Example Subroutine: Adding Two Numbers

• Scenario: A form with two text boxes for input, a button to sum the values, and a text box for the result.

• Code: الإجراء يقرأ القيم من مربعي النص، ويجمعهما بعد تحويلهما إلى أعداد صحيحة، ثم يعرض النتيجة في مربع نص آخر.

  Private Sub CmdSum_Click()
      Dim V1 As String
      Dim V2 As String
      Dim V3 As String
      Dim SUM As IntegerV1 = Text1.Text
  V2 = Text2.Text
  
  SUM = Cint(V1) + Cint(V2)
  V3 = CStr(SUM)
  
  Text3.Text = V3
  End Sub
  

Note: The Dim keyword is used to declare the variables.

Subroutine Example with Input and Output

Private Sub ConstructMessage(V As Integer)
    MsgBox "Value of V is = " & V
End Sub

Private Sub form_Load()
    V = InputBox("Enter a value (V)")
    ConstructMessage(V)
End Sub

• This subroutine ConstructMessage takes an integer V as input and displays a message box.

• MsgBox is a function that displays a dialog box with a message.

Functions

• Definition: A block of code that performs a specific task and returns a value.

• User-Defined Functions: Functions created by the programmer.

• Declaration: Starts with Private Function followed by the function name, parameters, and return type, and ends with End Function.

• Syntax:

  Private Function Fun_Name (Par1 As Type1, ..., Parn As TypeN) As Fun_Type
      ' Function body
      Fun_Name = ReturnValue ' Assign the return value
  End Function
  

  • Fun_Name: The name of the function.

  • Par1, ..., Parn: Parameters (inputs) to the function.

  • Type1, ..., TypeN: Data types of the parameters.

  • Fun_Type: Data type of the value returned by the function.

Returning a value:

Assign the return value to function's name inside the function body:

FunctionName = value

Example:

Private Function Message(Val As Integer) As String

Message = "The value of amount is " +Cstr(Val)

End Function

Notes: HAs StringI specifies the return value's data type.
*HValI specifies an input value. *
HIntegerI Specifies the input's data type.

• The return value can be String data type, and other data type

• Functions can also be used with HSUBI and SUBI @Îc@ and LHPrivate.

• Functions can also be used with HFunctionI @Îc@ and LHPrivate.

• End Function is used to close a function.

Predefined Functions:

• There are built in functions for Tools, Procedure.

Debugging

• Breakpoint: A marker in the code where execution pauses, allowing you to inspect variables and step through the code.

  • Toggle Breakpoint: F9. Or use Debug option.

  • View: Menu Bar, Add Watch.

  • Immediate Window: A window where you can execute commands and inspect variables during debugging (Ctrl+G).

Debug -> View -> Immediate Window

• Immediate Window: Can be used to find the values of variables by printing them.

• Print: Can be used to print variables in the immediate window.

Examples:

#1/1
My Age is 45

This part talks about error types.

• Logic errors, Compile errors, Runtime errors.

Also talks about how to fix them.

You can use the following in subroutines:
Exit.
Functions.
Or Call other functions.
Also you can create variables and use functions within one another to achieve modularity.
There are many ways of doing things.

Example with dividing the values.

Code:


Private Sub CmdDiv1_Click()

Dim num As Integer

Dim Den As Integer

Dim Res As String

num = Text1.Text

Den = Text2. Text

Res = Divide(num, Den)

If Res=!!!! Then

"Division by zero" = IblMini.Caption

Else

IblMini.Caption = Res

End If

End Sub


Private Function Divide (n As Integer, m As Integer) As String

If m = 0 Then

Exit Function

Else

Divide = " Division is " & n/m

End If

End Function

Built In Functions:

• Many prebuilt functions are available for performing tasks.

• Math.

• String related.

• Date and time related.

Example of Math functions:

Sqr(x)

• calculates the square root.

Number = Text 1. Text
Sqr = 5

Abs(x)

• Returns the absolute value of a number.

• Example: Abs(-45.6) returns 45.6.

Int(x)

• Returns the integer part of a number.

• Example: Int(332.54) returns 332.

Log(x)

• Returns the natural logarithm of a number.

• Example: Log(20) returns 2.9957327.

Sin(x)

• Returns the sine of an angle.

Cos(x)

• Returns the cosine of an angle.

Tan(x)

• Returns the tangent of an angle.

Example of String functions:

Len(String)

• Returns the length of a string.

Trim(String)

• Removes leading and trailing spaces from a string.

LTrim(String)

• Removes leading spaces from a string.

RTrim(String)

• Removes trailing spaces from a string.

Left(String, Length)

• Returns a specified number of characters from the left side of a string.

• Example: Left("How – are – you", 7) returns "How – a".

Right(String, Length)

• Returns a specified number of characters from the right side of a string.

• Example: Right("Have – A – Nice – Day", 8) returns "Nice – Day".

Mid(String, Start, Length)

• Returns a specified number of characters from a string, starting at a specified position.

• Example: Mid("Have – A – Nice – Day", 4, 8) returns "A – Nice".

Chr(Character)

• Returns the character associated with the specified ASCII code.

Str(String)

• Converts a number to a string.

Val(String)

• Converts a string to a number.

Date and time related Built in functions:

There are certain aspects related to formatting in other languages so I will skip it.

Now

• Returns the current date and time.

Date

• Returns the current date.

Time

• Returns the current time.

DateValue(DateTime)

• Returns the date part of a DateTime value.

TimeValue(DateTime)

• Returns the time part of a DateTime value.

Weekday(Date)

• Returns a number representing the day of the week (1 for Sunday, 7 for Saturday).

Format(Expression, Style)

• Returns a string formatted according to the specified style.

Year(Date)

• Returns the year part of a date.

• Example: Year(#18/6/2012#) returns 2012.

Month(Date)

• Returns the month part of a date.

• Example: Month(#18/6/2012#) returns 6.

Day(Date)

• Returns the day part of a date.

• Example: Day(#18/6/2012#) returns 18.