Mastering Looping Structures in Programming

1. Chapter 6 Looping Structures

2. 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

3. Infinite Loops • May have problems with loops • Logic error • Overflow error • Infinite Loop

4. 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

5. 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

6. 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)”)

7. For…Next Statement • Looping structure that performs a set number of times • Operates until a counter reaches an ending value

8. String Class • The string data type is a class containing multiple properties • String class properties:

9. 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

10. String Methods • Methods are procedures within a class .ToUpper .ToLower .Trim .TrimEnd .TrimStart .PadLeft(length,”char”) .PadRight(length, “char”)

11. String Substring • These return a portion of the string .Substring(startPos, numOfChars) .Remove(startPos, numOfChars) .Replace(oldString, newString) .Insert(startPos, substring) .IndexOf(substring)

12. String Class Examples Dim strSeason As String = “SummerTime” Dim strNewString As String strNewString = strSeason.ToUpper ‘SUMMERTIME strNewString = strSeason.ToLower ‘summertime strSeason = “ SummerTime “ strNewString = strSeason.Trim ‘SummerTime strNewString = strSeason.TrimEnd ‘ SummerTime strNewString = strSeason.TrimStart ‘SummerTime

13. Examples Cont… strSeason = “SummerTime” strNewString = strSeason.PadLeft(15, ”x”) ‘xxxxxSummerTime strNewString = strSeason.PadLeft(9, “x”) ‘SummerTime strNewString = strSeason.PadRight(13, “x”) ‘SummerTimexxx

14. Examples Cont… Dim strSeason As String = “SummerTime” Dim strNewString As String Dim intPos As Integer strNewString = strSeason.Substring(6,4) ‘Time strNewString = strSeason.Remove(0,6) ‘Time strNewString = strSeason.Replace(“Time”, “ is fun!”) ‘Summer is Fun strNewString = strSeason.Insert(6, “ is a fun “) ‘Summer is a fun Time intPos = strSeason.IndexOf(“mer”) ‘3

15. 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

16. 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)

17. 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

18. 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