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Chapter 6
Looping Structures
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Do…Loop Statement
• Can operate statements repetitivelyDo
intx=intx + 1
Loop While intx < 10– The Loop While operates the statement at least
once
Do While intx < 10
intx=intx + 1
Loop
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Infinite Loops
• May have problems with loops– Logic error– Overflow error– Infinite Loop
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Input Box
• Pop-up text box that allows the user to input information
• Has a prompt, text box, OK and cancel button
• How to display:strx = InputBox(“prompt”, “title”)intx = val(strx)me.lbl.text = intx
• If text box is blank = nothing
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Accumulator Variables
• Variable that stores an accumulating score
• Keeps a running total or sum
• Just like a counter
intTotal = intTotal + intScore
• Keep in mind if you’re adding decimals or integers
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Flags or Sentinels
• Something significant in your program that stops program execution or ends a loop
• Generally declared as a constant
• Inputbox(“Enter a positive number (-1 to finish)”)
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For…Next Statement
• Looping structure that performs a set number of times
• Operates until a counter reaches an ending value
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String Class
• The string data type is a class containing multiple properties
• String class properties:
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String Class
Example:
• Think of a String as a row of numbered boxes. The first boxe’s number is zero and they go up from left to right. Only one letter can be in each box.
0 1 2 3 4 5
S U M M E R
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String Methods
• Methods are procedures within a class.ToUpper.ToLower.Trim.TrimEnd.TrimStart.PadLeft(length,”char”).PadRight(length, “char”)
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String Substring
• These return a portion of the string
.Substring(startPos, numOfChars)
.Remove(startPos, numOfChars)
.Replace(oldString, newString)
.Insert(startPos, substring)
.IndexOf(substring)
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String Class Examples
Dim strSeason As String = “SummerTime”Dim strNewString As String
strNewString = strSeason.ToUpper ‘SUMMERTIMEstrNewString = strSeason.ToLower ‘summertime
strSeason = “ SummerTime “strNewString = strSeason.Trim ‘SummerTimestrNewString = strSeason.TrimEnd ‘
SummerTimestrNewString = strSeason.TrimStart ‘SummerTime
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Examples Cont…
strSeason = “SummerTime”strNewString = strSeason.PadLeft(15,
”x”) ‘xxxxxSummerTime
strNewString = strSeason.PadLeft(9, “x”)‘SummerTime
strNewString = strSeason.PadRight(13, “x”)
‘SummerTimexxx
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Examples Cont…
Dim strSeason As String = “SummerTime”Dim strNewString As StringDim intPos As Integer
strNewString = strSeason.Substring(6,4) ‘TimestrNewString = strSeason.Remove(0,6) ‘TimestrNewString = strSeason.Replace(“Time”, “ is fun!”)
‘Summer is FunstrNewString = strSeason.Insert(6, “ is a fun “)
‘Summer is a fun Time
intPos = strSeason.IndexOf(“mer”) ‘3
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String Concatenation
• Join two or more strings together
• String.concat(string1, string2)
• The & operator also joins strings
• To add spaces use empty quotes orSpace(#)
• The Space function will add a stated number of spaces
• vbTab adds 8 spaces, vbCrLf - returns
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Char Structure
• A structure is a simple form of a class
• Like the class, a structure has properties
chr1 = char.ToUpper(chr2)
chr3 = char.ToLower(chr2)
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Comparing Strings
• Used to alphabetize a list
• Compare(string1,string2,Case-insensitive)– Case-insensitive should be true or false
• True-case is not considered, a, A
• 0-string1 and string 2 equal
• 1-string1 is after string2
• -1-string1 is before string2
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Like Operator
• The Like is used as a Boolean expression– String1 Like String2– True if String1 matches the pattern of String2– False if there is no match– ? Used for a single character– * used for many characters– # used for a single number– [] used to enclose a list of characters– used to indicate a range of characters in a character
list– , used to separate characters in a character list