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Chapter 6. Looping Structures. Do…Loop Statement. Can operate statements repetitively Do intx=intx + 1 Loop While intx < 10 The Loop While operates the statement at least once Do While intx < 10 intx=intx + 1 Loop. Infinite Loops. May have problems with loops Logic error - PowerPoint PPT Presentation
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Chapter 6
Looping Structures
Do…Loop Statement
• Can operate statements repetitivelyDointx=intx + 1Loop While intx < 10
– The Loop While operates the statement at least once
Do While intx < 10intx=intx + 1Loop
Infinite Loops
• May have problems with loops– Logic error– Overflow error– Infinite Loop
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
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
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)”)
For…Next Statement
• Looping structure that performs a set number of times
• Operates until a counter reaches an ending value
String Class
• The string data type is a class containing multiple properties
• String class properties:
String ClassExample:
• 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 5S U M M E R
String Methods
• Methods are procedures within a class.ToUpper.ToLower.Trim.TrimEnd.TrimStart.PadLeft(length,”char”).PadRight(length, “char”)
String Substring
• These return a portion of the string.Substring(startPos, numOfChars).Remove(startPos, numOfChars).Replace(oldString, newString).Insert(startPos, substring).IndexOf(substring)
String Class ExamplesDim 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
Examples Cont…
strSeason = “SummerTime”strNewString = strSeason.PadLeft(15,
”x”) ‘xxxxxSummerTimestrNewString = strSeason.PadLeft(9, “x”)
‘SummerTimestrNewString = strSeason.PadRight(13,
“x”)‘SummerTimexxx
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 TimeintPos = strSeason.IndexOf(“mer”) ‘3
String Concatenation
• Join two or more strings together• String.concat(string1, string2)• The & operator also joins strings• To add spaces use empty quotes or
Space(#)• The Space function will add a stated
number of spaces• vbTab adds 8 spaces, vbCrLf - returns
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)
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
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