Visual Basic 6 Library Functions – String Type

These are the Built in Functions provided by Visual Basic. VB offers a rich set of built-in-functions for manipulating strings, numbers, dates and time. Built in functions are important and useful as they cut down effort and time, if one has to write the entire program all over. This tutorial is going to cover some of the important and commonly used string functions available in the Visual Basic Library.

String Functions
The string functions allow you to work with strings in numerous ways such as changing cases, extracting characters from a string, determining whether a character is a part of a string etc. etc.

1. The LCase and UCase Functions

these two functions convert strings to all lower or all upper case. The LCase( ) functions converts a string into all lower case and UCase( ) does exactly the opposite. These functions might be useful if you want to compare strings.

The Syntax would be :-


Consider the following example :-

The output would be HELLO WORLD.

Similarly,

Will produce string students.

Note that both the functions work ignorant of the fact whether the string has upper or lower case characters or not. They simply convert all the characters to upper or lower case respectively.

Now consider the following example.

Example 1.1
Obtain text from textbox txtLocation and determine whether the user lives on Earth or not. Remember that the user can enter the location in any possible case combination. You should be able to compare with all cases .

Essential Fact:
Note that it is essential for both stings to be equal in case as WELL as in LENGTH. Try running the Above code with a trailing blank in the text box, you wont get any result. Handling such problems is discussed further in the tutorial. You can also use LCase function (on both sides of course) instead of the UCase function that has been used in the above example. Always remember that you can compare strings in two ways; case – ignorant or non ignorant, depending on the need.

2. The Len Function

This Function gives you the length of the string i.e. how many characters long the string is. All the characters are counted ( punctuation, numbers, alphabets, special characters and blank spaces. Etc)

The Syntax is:-


Consider this:

After the above code is executed the variable iResult stores the value 20 , which is inclusive of the blank spaces in the sAddress variable.

This function can be used very effectively in allowing minimum and maximum length for a value. For example, a password field may have a minimum of 6 characters and a maximum of 20 characters, and this can be verified by the Len( ) Function.

3. The Trim, LTrim and RTrim Functions.

These functions remove leading (LTrim function) or trailing(RTrim Function) from a string. These functions don’t affect any spaces between words. The Trim( ) function simply accomplishes both LTrim( ) and RTrim( ) function, i.e. removes all leading and trailing blanks.

Syntax

Users may inadvertently type spaces into a text box, and you can use these functions to account for that, but mostly the Trim( ) function is used with fixed-Length strings, user defined types, and Random Access Files.

Now consider the following code example:

the variable sResult will store the value “excel” in it. Here we’ve used a function as an argument for another function. This is commonly done and an efficient way to program.

Now let’s re-write the program of example 1.1
This time note that the blank spaces in front or back of text should not affect the result.

See, now the code works irrespective of the blank spaces in front or back of the main text.

4. Left and Right Functions

These are two functions that are used to extract a certain number of characters from the leftmost or rightmost portions of a string. These functions require two arguments L the original string, and the number of characters to extract from that string.

Syntax:


Now consider the following example code.


The above code produces the result:

The first word Samuel is printed because of the statement

see that it has been assigned to take the Pname string containing “Samuel Williams” and extract 6 leftmost characters from it. Similarly the code:

extracts 8 rightmost characters from the Pname string.

5. Mid Function and Mid Statement.
Mid function is used to extract characters from the middle of a string, we need three arguments here: the Original String, the place to Start Extracting characters, and the number of characters to extract.

Syntax


for example, the following code :


will print “Day”, starting from the 7th character extracting 3 characters including the start position character. Try changing the start position and no of characters values in the function and notice the different results obtained.
Also note that all characters are included in the operation.

The Mid Statement not only extracts the characters, but also replaces them with the text you specify. Since this is a statement and not a function, you don’t get a result, rather the action is completed for you,

For example, in the following code, an unscrupulous person typed in the variable sInput that “Green Day Sucks”, you can change it to “Green Day Rocks” by the following Code:



here we see that the position of “S” in “Sucks” is at 11 position from start, in the string “Green Day Sucks”, therefore we input “11” as start position to replace, and since there are 4 preceding unwanted characters, we input “5” as the total number of characters to be replaced. The ‘=’ character indicates by which string to replace which we write on the right hand side, which is “Rocks”

SEE the difference in the First Print and the second print. And by applying your own Kode LogiK, you can specify the start position, the number of characters to replace and the text to put in the original place.

Now consider an example that uses both Mid( ) function as well as Mid Statement.

-Write a function namely AltCap that receives a String argument and returns the string wherein each alternate character is in Uppercase.

Now add this code in the general declaration part of a form.


Now call the Function in a Command Button’s click( ) event.


The output would be produced as :
I WaNt tO Be a lEeT

Note that blank spaces are also “uppercased” in the function that we have used, which obviously doesn’t have any effect.

6. InStr Function

The InStr function searches for strings within strings.

Syntax


Where


Bringing to your attention:


By default VB6 will use the Binary method to compare strings unless explicitly specified.

Now Consider the Following Code.


InStr is a function and will return the position of the first occurrence of the search string . if the string is not found then it will return ‘0’.

Something more


7. Space Function

this function by itself produces a certain number of spaces.

Syntax


Consider the following example code.


the best use of Space( ) is to clear fixed length strings.
sRecord = Space(128)

8. String Function

this function is used for producing a string with certain number of repeating characters.
Syntax


ForExample, the following code


will return “AAAAAAAAAA”

Now consider this :




9. Str Function

this function converts a number into equivalent string.



The following example uses the Str Function to return a sting representation of a number.


10. Asc Function

This function is used to get a character’s equivalent ASCII code
Syntax



For Example the following code will print 68, the ASCII code of character “D”.


11. Chr Function
This function returns a String containing the character associated with the specified character code.

The Syntax


where the required charcode argument is a Long that identifies a character.


Now consider the following example:


12. StrReverse Function
This Function returns a string in which the order of a specified string is reversed. Its Syntax is

erk ! error in this reply, plz read the next one

This post has been edited by Xenon: 5 Nov, 2005 - 11:39 PM

Adding further to this tutorial, i'd like to post a programming exercise to implement the knowledge gained by this tutorial in form of some litle programs.
------------
exercise 1
------------
Create a simple program that will search for a word in a given line of text.
-Steps
-Open Visual Basic, create a new form,
-set the
Caption = "Search For Words"
ScaleHeight = 2820
ScaleWidth = 9150

now build the following interface,



where the controls
-cmdSearch = command button name

-txtText = the name text box in which the main text is entered which is the big box in the interface.
its properties are set as.
- multiline = true
-scrollbars = vertical

-txtWord - the small text box in which the word to be search for is entered.
-chkIgnore -case ignore checkbox option

here's the code try to follow it by the captions in it, it'd be better if you copied and pasted in VB and then try to follow the logic of the code by actual working of the program.

open the code window, and add this code for the click event of the command button cmdVerify.


if you need further explanation, just add a reply here and ill try to explain it with further details.

Hope this was useful

--------------
exercise 2
--------------
Create an application that will reverse the entered string input. DO NOT use the StrReverse() function.

-this add on will help you to understand the working of the strReverse() function.
----------
now build the following interface.

-------------
where the controls are
TextBox txtRev - the lower textbix in the form, which displays the reversed string

TextBox txtStr - input string box.

CommandButton cmdReverse - the code is the click event of this button.
-------------


the working
we use a For -- Next loop to achive our goal.
-First of all we feed the input string value to the string variable strl.

-Secondly, we store the length of the string in the length variable.

-next, we start the for loop, in which we start the loop in a reverse way.
that is we go from the last character of the string to the first.

-everytime, we extract ONE character using the MID function and put it in the textbox, one after the other in the line


also notice the begining of the for loop


step - 1 makes the for loop go one value less than the previous one every time, so the function takes the string backwards.
------------------
this is the same logic on which the StrReverse function works.

Kode LogiK
Xenon

here are some more functions that i forgot to mention....equally useful.

13. Replace Function

this function returns a string in which a specified sub-string has been replaced with an another substring a specifed number of times.

The SynTax is:-


where the expression:


Return Values

Replace returns the following values


14. StrComp Function
This Function returns a integer value after the comparison of two string expressions.

its syntax is :


where


the return value can be of 4 types.

I want this