© 2006 Lawrenceville Press Slide 1 Chapter 6 The Post-Test Do…Loop Statement Loop structure that...

© 2006 Lawrenceville PressSlide 1

Chapter 6Chapter 6The Post-Test Do…Loop The Post-Test Do…Loop

StatementStatement Loop structure that executes a set of statements as long as a condition is true.

The condition is a Boolean expression. Executes at least once. The terminating condition is checked after the

body of the loop is executed. The loop below iterates while sum is less than

10:sum = 0;Do

sum += 2Loop While sum < 10


Chapter 6Chapter 6Pre-Test Do…LoopPre-Test Do…Loop

Executes only if the condition is initially true. May not iterate at all.

The terminating condition is checked before the body of the loop is executed.

The statementsum = 20Do While sum < 10

sum += 2Loop

does not iterate at all because sum is initially greater than 10.


Chapter 6Chapter 6Infinite LoopsInfinite Loops

A loop that continues executing forever Can be caused by syntax or logic errors. For

example:num = -1Do

num -= 1 'num is decreased by 1While num < 0

Some errors result in an overflow causing a run-time error.


Chapter 6Chapter 6The InputBox FunctionThe InputBox Function

Displays a predefined dialog box that has a prompt, a text box, and OK and Cancel buttons, and then returns a string.

Used to obtain information from the user. The function is used as part of an assignment

statement:stringVar = InputBox(prompt,

title)

Clicking Cancel or leaving the text box blank returns Nothing.

The Val() function can be used to convert string data to numeric data.


Chapter 6Chapter 6Accumulator VariablesAccumulator Variables

A variable that is incremented by a varying amount. accumulator = accumulator + value

Often used for keeping a running total. intTotalScore = intTotalScore +

intNewScore intTotalScore += intNewScore

Should be initialized when declared.


Chapter 6Chapter 6Assignment OperatorsAssignment Operators

Operator Operation+= addition and then assignment-= subtraction and then assignment*= multiplication and then

assignment/= division and then assignment\= integer division and then

assignment^= exponentiation and then

assignment


Chapter 6Chapter 6Using FlagsUsing Flags

A flag, or sentinel, indicates when a loop should stop iterating.

Often a constant. Code is easier to modify when sentinels are

constants declared at the beginning of a procedure.


Chapter 6Chapter 6The For…Next StatementThe For…Next Statement

Loop structure that executes a set of statements a fixed number of times.

Uses a counter to control loop iterations. The keyword Step can optionally be used to

change the amount the counter is incremented or decremented.

The loop below executes until num is equal to 10:

For num As Integer = 0 To 10i += num

Next num


Chapter 6Chapter 6The String ClassThe String Class

Includes properties and methods. A String object is comprised of a sequence of

characters with the first character at index position 0.

String properties include:Chars(index)Length()


Chapter 6Chapter 6String MethodsString Methods

String methods for manipulating a string include:

ToUpper converts a string to all uppercaseToLower converts a string to all lowercase Trim removes spaces from the beginning

and end of a string

TrimEnd removes spaces from the end of a string

TrimStart removes spaces from the beginning of a string

PadLeft(len, char) adds a specified character

to the beginning of a string until the string is

len characters longPadRight(len, char) adds a specified

characterto the end of a string until the string is

lencharacters long


Chapter 6Chapter 6String Methods String Methods ((cont.cont.))

String methods for manipulating a substring:Substring(startPos, numOfChars)

returns the substring that is numOfChars in

length and starts at startPosRemove(startPos, numOfChars)

deletes the substring that is numOfChars in

length and starts at startPos Replace(oldString, newString)

exchanges every occurrence of oldString

with newString Insert(startPos, substring)

inserts substring at startPos IndexOf(substring)

returns the first position of substring


Chapter 6Chapter 6String ConcatenationString Concatenation

Concatenation is joining two or more strings together.

The String method Concat() joins two or more strings. It is a shared method and must be used with the String class, not an object of the class:s = String.Concat("this","and","that")

The &= operator concatenates a string to an existing string:

s = "thisand"s &= "that"

The & operator concatenates strings:s = "this" & "and" & "that"


Chapter 6Chapter 6String Concatenation (String Concatenation (cont.cont.))

Dim strSeason As String = "SummerTime"Dim strMessage As String = " is a fun time!"Dim strNewString As String

'SummerTime is a fun time!strNewString = String.Concat(strSeason, strMessage)

Dim strFirstName As String, strLastName As StringDim strFullName As String

strFirstName = "Elaine"strLastName = "Malfas“'Elaine MalfasstrFullName = strFirstName & " " & strLastName


Chapter 6Chapter 6Space(), vbTab, vbCrLfSpace(), vbTab, vbCrLf

The Space() function returns a string of spaces. vbTab is a built-in constant that represents 8

spaces. vbCrLf is a built-in constant that represents a

carriage return-linefeed combination.


Chapter 6Chapter 6The Char StructureThe Char Structure

A simple form of a class. Char has two shared methods:

ToUpper()ToLower()

The methods must be used with the Char structure:

newLetter = Char.ToUpper(letter1)


Chapter 6Chapter 6UnicodeUnicode

A digital code with representations for every character in every language and symbol. Table with some examples : pg. 6-15

Two built-in functions for converting between characters and Unicode:

AscW(char)ChrW(integer)


Chapter 6Chapter 6Comparing StringsComparing Strings

When relational operators (=, >, <, >=, <=, <>) are used to compare strings, their Unicode values determine the relationship between the strings.

The Compare() method is a better choice to alphabetically compare strings:Compare(string1, string2, case-insensitive)

returns 0 if string1 and string2 are the same. A

positive number is returned if string1 is greater

than string2 and a negative number if string1 is

less than string2. case-insensitive should be

true if the case of the strings should not beconsidered.


Chapter 6Chapter 6The Like OperatorThe Like Operator

Used to perform a textual comparison between two strings.

Can be used to perform pattern matching. The pattern can include:

? used in place of any single character

* used in place of many characters# used in place of any single number[] used to enclose a list of characters- used to indicate a range of

characters in a list

, used to separate characters in a list

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