BACS 287 Visual Basic String Manipulation

BACS 287 Visual Basic Strings In Visual Basic, a “string” is a series of text, numbers, and special characters. Strings are stored in string variables. String values are always enclosed in quotation marks. There is only 1 built-in operator that works on strings (the ‘&’ operator).

BACS 287 String Characteristics  All strings in Visual Basic are variable-length strings.  A variable-length string can contain up to approximately 2 billion characters.  Generally speaking, string variables can contain any character represented on the keyboard.

BACS 287 String Examples The following are examples of defining and manipulating strings. Dim strInput as string = “ABC 123” Dim strOutput as string = “def,/ 56r” Dim strX as string strX = strInput & strOutput Results in strX value of “ABC 123def,/ 56r”

BACS 287 Operations on Strings There are 2 basic ways to manipulate strings in Visual Basic – Using built-in string functions – Using string methods Methods associated with string variables are the more modern way to manipulate strings You can use either methods or functions; both achieve the same results; however, methods are the preferred way.

BACS 287 String Methods There are several methods automatically associated with all string variables. Determine current string state: string.Length – returns the number of characters in a string string.Compare – determine if two strings are the same string.IsNullOrEmpty – determine if a string is null or empty string.StartsWIth – determine if a group of characters is at start of a string string.EndsWith – determine if a group of characters is at end of a string string.Contains – determine if a string contains a group of characters (Boolean) string.IndexOf – find the starting location of a substring within the string

BACS 287 String Methods Modify edges of string: string.TrimStart – removes leading characters from a string string.TrimEnd – removes trailing characters from a string string.Trim – removes leading and trailing characters from a string string.PadLeft – adds characters to the beginning of a string string.PadRight – adds characters to the end of a string Convert string to different format: string.ToUpper – convert all characters to upper case string.ToLower – convert all characters to lower case

BACS 287 String Methods Add / Remove characters in existing string: string.Remove – removes characters from anywhere in a string string.Substring – extract a substring from the string string.Replace – replaces characters with other characters in a string string.Insert – adds characters within a string Manipulate string into different string / array: string.CopyTo – copies a specified number of characters to an array string.Split – returns a string array of delimited elements from the original string

BACS 287 String Functions Most of the same string manipulations can be performed with system defined functions. INSTR - returns the position of the first occurrence of one string within another MID - Returns the specified number of characters from a string LEN - Returns the number of characters in a string LEFT / RIGHT - Returns the specified number of characters from the left/right side of a string. UCASE / LCASE - Returns a string that has been converted to uppercase or lowercase

BACS 287 String Functions TRIM / RTRIM / LTRIM - Returns a copy of a string without leading spaces (Ltrim), trailing spaces (Rtrim), or both leading and trailing spaces (Trim). FORMAT - Formats an expression according to instructions contained in a format expression.

BACS 287 InStr Function The InStr function is used when you want to find the first occurrence of one string within another. It returns the position of where the match is found, 0 if it is not found. Syntax: InStr (start, string1,string2,[compare]) NOTE: You start counting at 1 with this command

BACS 287 InStr Function Example SearchString ="XXpXXpXXPX XP“ ' String to search in (note that position 11 is a space). SearchChar = "P"' Search for "P". IntStartPos = 7‘ Start in position 7 ' A textual comparison starting at position 4. Returns 6 MyPos = InStr(4, SearchString, SearchChar, 1) ' Comparison is binary by default (last argument is omitted). MyPos = InStr(SearchString, SearchChar)' Returns 9 MyPos = InStr(1, SearchString, " ") ' Returns 11 (started in pos 1) MyPos = InStr(intStartPos, SearchString, "p")' Returns 0 (did not find it)

BACS 287 Mid Function The MID function is used to extract characters from a string. It is commonly used with InStr to pull out the sub-string that was located. Syntax: Mid (string, start, [length])

BACS 287 Mid Function Example MyString = "Mid Function Demo"' Assign text string. FirstWord = Mid(MyString, 1, 3)' Returns "Mid". LastWord = Mid(MyString, 14, 4)' Returns "Demo". MidWords = Mid(MyString, 5)' Returns "Function ' Demo". strOut = Mid(MyString, InStr(1,MyString,”F”), 8) ' Returns “Function” InStr function returns 5

BACS 287 Determine String Length The Length method and the Len function may be used to determine the number of characters in a string. The Len function can also be used to determine the number of bytes to store a variable (somewhat obscure). Syntax: string.length Len (string | variable)

BACS 287 Determine String Length Example Dim MyString as string = “Hello World” Dim MyInt As Integer Dim MyCur As Currency ‘ use method MyLen = MyString.Length‘ returns 11 ‘ use function MyLen = Len(MyString)' Returns 11. MyLen = Len(MyInt)' Returns 2. MyLen = Len(MyCur)' Returns 8.

BACS 287 Modify String Edges Operations The Left and Right functions are used to extract characters from the left and right side of a string. The original string is not modified Syntax: Left (string,length) Right (string,length)

BACS 287 Left / Right Example AnyString = "Hello World"' Define string. MyStr = Left(AnyString, 1)' Returns "H". MyStr = Left(AnyString, 7)' Returns "Hello W". MyStr = Left(AnyString, 20)' Returns "Hello World". MyStr = Right(AnyString, 1)' Returns "d". MyStr = Right(AnyString, 6)' Returns " World". MyStr = Right(AnyString, 20) ' Returns "Hello World".

BACS 287 Ucase / Lcase Function The Ucase and Lcase functions return a string with the case changed to upper or lower. Syntax: Ucase (string) Lcase (string)

BACS 287 Ucase / Lcase Example strInput = "Hello World 1234" ' String to convert. UpperCase = UCase(strInput) ' Returns "HELLO WORLD 1234". LowerCase = LCase(strInput) ' Returns ”hello world 1234".

BACS 287 Ltrim / Rtrim / Trim Function The Ltrim, Rtrim, and Trim functions remove leading spaces, trailing spaces, and both leading and trailing spaces. Syntax: LTrim (string) RTrim (string) Trim (string)

BACS 287 LTrim / Rtrim / Trim Function MyString = " "' Initialize string TrimString = LTrim(MyString)' TrimString = " ". TrimString = RTrim(MyString)' TrimString = " ". TrimString = LTrim(RTrim(MyString)) ' TrimString = " ". ' Using the Trim function alone achieves the same result as the previous example. TrimString = Trim(MyString)' TrimString = " ".

BACS 287 Format Function The Format function is used format a string expression based upon instructions given in a “format expression”. The rules for this function are very complex and are best learned via the VB help screens. Syntax: Format(expression,[format,[firstdayof week,[firstweekofyear]]])

BACS 287 Format Function Examples MyTime = #17:04:23# MyDate = #January 27, 1999# ' Returns current system time in the system-defined long time format. MyStr = Format(Time, "Long Time") ' Returns current system date in the system-defined long date format. MyStr = Format(Date, "Long Date") MyStr = Format(MyTime, "h:m:s")' Returns "17:4:23". MyStr = Format(MyTime, "hh:mm:ss AMPM")' Returns "05:04:23 PM". MyStr = Format(MyDate, "dddd, mmm d yyyy")' Returns "Wednesday, ' Jan ".

BACS 287 Format Function Examples ' If format is not supplied, a string is returned. MyStr = Format(23)' Returns "23". ' User-defined formats. MyStr = Format(5459.4, "##,##0.00")' Returns "5,459.40". MyStr = Format(334.9, "###0.00")' Returns "334.90". MyStr = Format(5, "0.00%")' Returns "500.00%". MyStr = Format("HELLO", "<")' Returns "hello". MyStr = Format("This is it", ">")' Returns "THIS IS IT". See Visual Basic help screens for more format expression details.

BACS 287 Nesting String Functions You can nest string functions inside each other. The innermost function is performed first and the outermost is performed last. Example: Dim MyString as string = ” nested function demo “ strX = Mid(Ucase(Trim(MyString)), InStr(1,Ucase(Trim(MyString)),”UNC”), 8) ' Returns “UNCTION ”

BACS 287 Nesting String Functions This also works with string methods. Example: Dim MyString as string =” nested function demo “ strX = MyString.Substring((MyString.Trim.ToUpper.IndexOf("UNC", 0) + 2), 8).ToUpper ' Returns “UNCTION ”