Strings PART I

1. StringsPART I STRINGS, DATES, AND TIMES

2. FUNDAMENTALS OF CHARATERS AND STRINGS • VB represents characters using American National Standards Institute(ANSI) Character Set • Small integer values 0 to 127(1st 128 ANSI Characters) equal American Standard Code for Information Interchange(ASCII) • Strings are series of characters treated as single unit • include: letters, numbers, special characters, and others (special VB data type)

3. FUNDAMENTALS OF CHARATERS AND STRINGS • String literals or string constants indicated by double quotes • Example: “John Q. Doe” • “9999 Main Street” • “Somewhere, Massachusetts” • “(555) 555-5555” • Dollar sign is type declaration character for String • String data type: • declares string variables

4. FUNDAMENTALS OF CHARATERS AND STRINGS • Types of strings: • 1. variable-length (default) • 2. fixed-length • Consists of characters with numeric values, range 0 to 255 • grow and shrink dynamically • Example: Variable-length • Dim s As String • s = “blue”

5. FUNDAMENTALS OF CHARATERS AND STRINGS • Example: Fixed length • Dim SocialSecurityNumber As String * 11 • SocialSecurityNumber = “212-45-6363” • String Concatenation with & and + : • combine smaller strings into one • Example: s1 = “Pro” • s2 = “gram” • s3 = s1 & s2 output=program • or s3 = s1 + s2

6. FUNDAMENTALS OF CHARATERS AND STRINGS • Problem: s1 = “hello” + 22 • would attempt convert hello to number and • add 22 resulting in type mismatch • Rule of thumb: use & for concatenation • Comparing Character Strings: • use: relational operators (<, >, <= , >=) • equality operators (<>, =)

7. FUNDAMENTALS OF CHARATERS AND STRINGS • StrComp function: • returns: 0 if strings are equal • -1 if 1st string is < 2nd string • 1 if 1st string is > 2nd string • Comparisons are made based on numeric values (ASCII) associated with characters • Function StrComp has an optional 3rd argument: • indicates comparison type

8. FUNDAMENTALS OF CHARATERS AND STRINGS • Option Compare type (module-level statement) • type: Binary, Text, or Database • Option Compare not used: default is Binary • Strings of different length: • Example: “j” VS. “john” • if one name is equivalent to leftmost portion of another name, shorter name comes before longer name

9. FUNDAMENTALS OF CHARATERS AND STRINGS • Operator Like • another comparison of two strings • compare patterns of characters as well as strings • Example: “HBLT55DD” Like “HBLT55DD” • True or False test • “HBLT55DD” Like “HBLT*” • asterisk is pattern matching character • any number of characters can follow

10. FUNDAMENTALS OF CHARATERS AND STRINGS • question mark- single character can be any type of character • pound sign- single character can be a digit • Example: “HBLT55DD” Like “?#LT55DD” (false) • “HBLT55DD” Like “?BLT##DD” (true) • square brackets- series of characters provided for matching characters • Example: “HBLT55DD” Like “H[A-F]LT55DD” • “HBLT55DD” Like “H[A-F]LT[!4-7]5DD” [!] not

11. MANUIPULATING INDIVIDUAL CHARACTERS • Code example: Figure 8.3, p. 310 • Mid$ - allows programmer to extract one character at a time from a string • Example: Figure 8.4, p. 311 • Mid$ used with phrase to extract one character at a time in reverse • Note1: program also uses Len function to determine length of phrase

12. MANUIPULATING INDIVIDUAL CHARACTERS • Mid$ Function Arguments: • 1. Source string from which substring will be selected • 2. Starting character position in string • 3. Number of characters to select • Note2: if last argument is omitted or number of characters remaining is less than number of characters, remainder of string from starting character position is returned

13. MANUIPULATING INDIVIDUAL CHARACTERS • Example: phrase = txtInput.Text • txtOutput.Text = txtOutput.Text & _ • Mid$ (phrase, position, 1) • Note3: can be used to replace portion of string with another string • Example: x =“Visual Basic 6!” • Mid$ (x,2,3) = “xxx” • x changed to “Vxxxal Basic 6!”

14. LEFT$,RIGHT$, AND INSTR • Left$ selects left most portion of string • Example: s1=“ABCDEF” • s2=“Left$(s1,4) • Assigns leftmost four character to s2 • s2 = “ABCD” • Right$ selects rightmost portion of string • s1 = “ABCDEF” • s2 = Right$(s1,4) • Assigns rigthmost four characters to s2

15. LEFT$,RIGHT$, AND INSTR • s2 = “CDEF” • InStr search through one string (base string) to determine if it contains another string (search string) • When found, starting character location of string is returned • Should second string contain no character (0 length), starting position is returned • Example: s1 = “AEIOU” • s2 = “IOU”

16. LEFT$,RIGHT$, AND INSTR • result = InStr(1, s1, s2) • result = “IOU” • (starts search at position 1 of s1) • Note1: If InStr determines search string is not contained within base string, returns zero • Example: result = InStr(1, “aeiou”, “aeb”) • result = InStr(4, “aeiou”, “iou”) • result = InStr(1, “aeiou”, “aeiouy”) • result = 0 for all three cases

17. LEFT$,RIGHT$, AND INSTR • (1) blankPosition = InStr(1, phrase, “ “) • returns first blank position in phrase • (2) nextWord = Left$(phrase, blankPosition - 1) • picks off one word at a time from phrase and assigned to nextWord • (3) phrase = Right$(phrase, Len(phrase) - blankPosition)

18. LEFT$,RIGHT$, AND INSTR • returns remainder of phrase from character after blankPosition • Note2: eventually phrase shrinks to one word • Searching for Substrings in Strings Using InStr and InstrRev: • search for substrings in a string from beginning to end of string • InStr searches from any location in a string • InStrRev search from end or any other position

19. Searching for Substrings in Strings Using InStr and InstrRev • InStrRev’s arguments: • (1) base string • (2) search string • (3) starting character position in base string • Outcome” • (1) if search string found, starting character location of string is returned • (2) if search string is zero length, starting position is returned

20. Searching for Substrings in Strings Using InStr and InstrRev • Example1: Dim s1 As string, s2 As string • s1 = “abcdefghijklmnop” • s2 = “m” • result = InStrRev (s1, s2, Len (s1)) • determines s2 is in s1 at position 13 • return 13 as starting position (s2 in s1) • 13 is assigned to result • Len (s1)- s2 begins at end of s1

21. Searching for Substrings in Strings Using InStr and InstrRev • Note: third argument can be omitted if search begins from end of base string • if string not contained in base string, returns 0 • Example2: result = InStr(“aeiou”, “aeb”) • result = InStr(“aeiou”, “iou”, 2) • resutl = InStr(“aeiou”, “aeiouy”) • fowardResult = InStr(Input1, Input2) • locates 1st occurrence of Input2 in Input1

22. Searching for Substrings in Strings Using InStr and InstrRev • backwardResult = InStrRev(txtInput1.Text, txtInput2.Text) • locates last occurrence of txtInput2.Text in txtInput1.Text starting from end of txtInput1 • LTrim$, Rtrim$, Trim$: • (1) remove leading spaces from left side of string • (2) remove trailing spaces from right side of string • (3) remove spaces on left and right side of string

23. Ltrim$, Rtrim$, Trim$ • Useful for removing extra space characters used to pad a fixed-length string • string would occupy space allocated • String$ and Space$: • create strings of specified number of characters • String$ creates string of specified character • Space$ creates string of spaces