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.