Beginner’s Guide to Visual Basic 6 – Part 2

In Part 1 we touched the basic’s, now we will move to the next step.

System Defined Functions: Now the second chapter, we will deal first with some of the system-defined functions in vb. What is this “function” ? Well a function is a special type of procedure that returns a value each time it is called. A function is generally used to perform a particular task/s repeatedly when needed. Visual basic provides several built-in functions as part of the programming language, such as MsgBox, Round and so on. We can also create our functions which does a user defined task. We can pass arguments to that function and return a value also based on the parameters. There are 4 types of functions in Visual Basic and they are as follows

  1. Conversion Functions
  2. String Functions
  3. Application Enhancement Functions
  4. Date Functions

Conversion Functions: As the name indicates these functions are used to convert one datatype variable to another datatype. The functions are as follows

Function Description
Asc Returns a character code corresponding to the first letter of a given string.
Chr Return the character associated with the specified character code.
Cbool Converts an expression to boolean.
Cbyte Converts an expression to byte
Ccur Converts an expression to currency
Cdate Converts an expression to date
CDbl Converts an expression to double
Cint Converts an expression to Integer
Clang Converts an expression to long
CSng Converts an expression to single
CStr Converts an expression to string
Cvar Converts an expression to variant
Str Returns the string representation of a number
Val Returns number equivalent of a string

Syntax:
Function_name <expression/string/number>

Function_name is the conversion function to be used
Expression/string/number is the input given to the conversion function

String Functions: A String variable can be of fixed length or variable length. You know that the default size of the string depends on the text assigned to it. Visual basic has more than 45 functions for string manipulation but the most commonly used examples are as follows

  1. Trim
  2. StrReverse
  3. StrComp
  4. InStr
  5. Mid
  6. Lcase

Trimming a String: The following three functions are used to return a copy of a string without spaces

  1. LTrim
  2. RTrim
  3. Trim

Example:

sVar1=" Hello " 'Assume this is the string you have
 
sLTrimVar = Ltrim(sVar1) 'returns "Hello "
sLTrimVar = RTrim(sVar1) 'returns " Hello "
sLTrimVar = Trim(sVar1) 'returns "Hello "

Comparing Strings: Strings can be compared for their value by using the StrComp function and the Like operator.

Syntax:

StrComp (String1, String2, [compare type])
'String1 is any valid string
'String2 is any valid string

Compare type is an optional argument that specifies the type of comparison. You can compare the textual value or do a binary comparison on the string. In compare we can give three types of compares which are

  1. VbBinaryCompare (Does a byte by byte comparison, is case sensitive)
  2. VbDatabaeCompare (Compare information inside database)
  3. VbTextCompare (Does case insensitive compare)

Example:

Dim sVar1 as String, sVar2 as String
SVar1=”NETHS”
SVar2=”neths”
MsgBox StrComp(sVar1, sVar2, VbBinaryCompare) ‘Returns –1
MsgBox StrComp(sVar1, sVar2, VbTextCompare) ‘Returns 0

Reversing Strings: Strings can be reversed using the function StrReverse function. This function returns the character of the specified string in reverse order

Syntax:

StrReverse (String1)

Example:

Dim sResult As String
 
sResult = StrReverse("Hello Nethaji")
Msgbox sResult 'displays ijahteN olleH

Search Functions: The InStr function is used to return the position of the occurrence of a string within another string.

Syntax:
InStr ([start position], String1, String2, [compare-type])

Start position is a numeric expression indicating the starting position for the search. If this is not specified it search starts from the first character. The start position and compare-type are optional. The compare types are similar to that of the StrComp Function.

Example:

Dim sVar1 As String, sVar2 As String
 
sVar1 = "Hello Nethaji, It's a nice day"
sVar2 = "nethaji"
 
MsgBox InStr(1, sVar1, sVar2, VbBinaryCompare) 'Returns 0
MsgBox InStr(1, sVar1, sVar2, VbTextCompare) 'Returns 7

String Extraction: This function allows you to replace the characters at any arbitrary location in a string.

Syntax:
Mid (sSourceString, StartPosition, Length)

Example:

Dim sVar1 As String
 
sVar1 = "Nethaji is Coding"
MsgBox Mid(sVar1, 1, 7) 'Displays Nethaji

Visual Basic offers 45 string functions, some of which have been explained. The rest I leave you to find and explore.

Date Functions: The calculation and modifications of dates can be done with certain date functions and modifications to the time part of a Date variable. VB offers 25 date functions. Some of the commonly used functions are listed below.

Function Syntax Description Example
Date Date Returns Current Date Msgbox Date
Now Now Returns current date and time. Msgbox Now
Day Day(Date) Returns a numeric representation of current day. Msgbox Day(Date)
Month Month(Date) Returns a number between 1 and 12 representing a month. MsgBox Month(Date)
DateAdd Date(interval,number,date) Returns a variant containing a date to which a specified time interval has been added. The interval can be
y,q,m,w,d,h,s
MsgBox DateAdd(“d”, 1, Date)
DateDiff DateDiff(interval,date1,date2) Returns the number of time intervals between two dates. MsgBox DateDiff(“d”, “13-June-99”, “14-June-99”)

Note: The parameter “d” indicates interval in days. In the same lines we have the following list

  • “n” returns in minutes
  • “h” returns in Hours
  • “m” returns in months
  • “y” returns in years
  • “s” returns in seconds

Application Enhancement Functions: In windows-based applications, dialog boxes are used to prompt a user for appropriate date or to display information for users. Visual basic allows you to create dialog boxes with predefined functionality. Msgbox and InputBox are the functions for creating such dialog boxes. These dialog boxes must be closed before you continue to work on the rest of the application. These are also called modal dialog boxes.

Msgbox Function: A modal Dialogbox with a predefined set of buttons (from which you can choose). You can click this link for a detailed study on the constants.

Syntax:
Msgbox (prompt,[buttons],[title],[helpfile-context])

Example:

Msgbox (“Hi Nethaji”,vbOkOnly,”Nethaji’s First Msgbox”)

InputBox Function: The InputBox function displays a prompt in a dialog box and waits for the user to enter text. The function returns the text that has been entered by the user.

Syntax:
InputBox (prompt, [title], [default], [xpos], [ypos])

Example:

MsgBox InputBox("Your Age", "Nethaji's Age", "67")

Control Structures: Control structures enable you to execute a certain set of statements based on a condition. The condition should be specified at the design time. At runtime, the condition is evaluated, and depending on the result of the condition, the block of code following the condition is executed. These structures are also known as decision structures. These include the If….. Then…Else and the Select Case.

If ………. Then ………. Else Statement

You can use the if statement where there is a need to execute a statement of a set of statements based on a condition. For instance here’s a sample if statement that checks whether the value of the variable is greater than 10.

If iVar1 &gt; 10 then
Msgbox “iVar1 greater than 10”
Else
Msgbox “iVar1 lesser than 10”
End if

One more thing is that you can nested Ifs that is an if Within an If. We also have something called Else Ifs, Here’s an example of it.

If iVar1=1 then
Msgbox “iVar1 is 1”
Elseif iVar1=2 then
Msgbox “iVar1 is 2”
Elseif iVar1=3 then
Msgbox “iVar1 is 3”
Else
Msgbox “iVar greater than 3”
End if

Select Case Another alternative to the If. Else statement is the Select Case statement. Here’s an example to illustrate my point

Example:

Select Case iVar1
Case 1
Msgbox “iVar is 1”
Case 2
Msgbox “iVar1 is 2”
Case 3
Msgbox “iVar1 is 3”
Case Else
Msgbox “iVar greater than 3”
End Select

Loop Structures: Looping structures are used when a group of statements is to be executed repeatedly, based on a condition. There are 4 types of loop structures in VB, and they are as follows

  1. Do. Loop
  2. While.. Wend
  3. For.. Next
  4. For Each.. Next

Do.. Loop This loop construct is used to repeat the execution of a block of statements based on a condition. This loop construct evaluates a condition to determine whether or not to continue the execution. There are 4 ways a Do. Loop can be written.

1. Do While <condition>
<Statements>
Loop

Tests the <condition> first and, if true, executes the <statements> loops based on condition.

2. Do
<Statements>
Loop While

Executes the <statements> first and then tests the <condition> Loops at least once, then tests the condition

3. Do Until
<Statements>
Loop

Tests the <condition> first and, if False, executes the <statement> Loops till the condition if False

4. Do
<Statements>
Loop Until

Executes the <statements> and then tests the <condition> Loops at least once, then tests the condition Executes till the condition is False.

Example:

Dim iCnt As Integer
Do While iCnt &lt;= 10
MsgBox iCnt
iCnt = iCnt + 1
Loop ‘This loop executes till the value of iCnt reaches 10

While. Wend Loop The While. Wend loop structure allows you to perform a series of steps based on a condition.

Syntax:

While <condition>
<Statements>
Wend

Example:

Dim iCnt As Integer
While iCnt &lt;= 10
MsgBox I
iCnt = iCnt + 1
Wend
'This loop executes till the value of iCnt reaches 10

For.. Next Loop: The For .. Next loop uses a counter that increases or decreases the value of a variable each time the loop is executed.
Syntax:

For <Counter>=<Start> To <End> [Step Value]
[Statements]
Next <Counter>

Some examples for “for” loops are

'First
Dim iCnt As Integer
 
For iCnt = 0 To 10
MsgBox iCnt
Next iCnt
 
'The loop executes till iCnt reaches 10. It is not necessary to give "Next iCnt", as the loop automatically increments the value.
 
'Second
Dim iCnt As Integer
 
For iCnt = 0 To 10 Step 2
MsgBox iCnt
Next
 
'The end result will be the same but if you notice you will be displayed on even number that is iCnt is always incremented by 2. That’s the use of Step keyword.

For Each.. Next Loop
The For Each.. Next loop is used to perform an operation on each element of an array or collection.

Dim sCollection As New Collection
Dim sCurItem As Variant
 
sCollection.Add ("ProgrammingFundas.com")
sCollection.Add ("NonStopSense.Net")
sCollection.Add ("VBCity")
 
For Each sCurItem In sCollection
MsgBox sCurItem
Next

With.. End With You can write a number of code statements that act on the same object. To make this type of code more efficient and easier to read, we can use the With and End With statement. The statement allows you to set multiple properties and call multiple methods quickly and easily. Since the object is referenced only once, the code executes faster.

Example:

With TxtName
.Font.Italic = True
.Font.Size =24
.Text = “Hello Nethaji”
End With

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