* Test for a condition being true or false

* Expression is called a Boolean expression because it evaluates to either true or false. If expression is true, execute statements...otherwise statements are skipped

if decSales > 5000

MessageBox.Show("You've earned a bonus!")

End if 

*Determines if a specific relationship exists between two values 

>     Greater than

<      Less than  

=      Equal to

<>      Not equal to

>=      greater than or equal to

<=               less than or equal to

*In a stand alone statement = is interpreted as assignment.

intUserNumber = 45

*In a Boolean expression = is interpreted as comparison

If intUserNumber = 45 Then

Function Calls in Expressions 

If CInt(txtInput.Text) < 100 Then

lblMessage.Text = "It is true!"

End If

If blnQuotaMet Then

lblMessage.Text = "You have met your sales quota"

End if 

* Note that since a Boolean variable already evaluates to true or false, an = operator is not required 

If expression Then

statements

Else

statments

End if 

If decSales > 5000 Then

MessageBox.Show("You've earned a bonus!")

Else 

MessageBox.Show("No bonus")

End If

If it is very cold Then

Wear a coat

Elseif it is chilly then

wear a light jacket

Elseif it is windy then

wear a windbreaker

Elseif it is hot then

wear no jacket 

*Any type of statement can be used inside an if, including another if statement. If statements within if statements creat a more complex decision structure. 

If dblSalary>30000 then 

If intYearsOnJob > 2 Then

lblMessage.Text = "Applicant qualifies."

Else 

lblMessage.Text="Applicant does not qualify."

End if

End if 

*We can combine two or more Boolean expressions into one. 

If intTemperature <40 And strSeason = "Summer" Then

lblMessage.Text = "It is unusually cold."

End if 

^^ Logical Operator 

*Combines multiple Boolean expressions into a compound expression

*And, or , xor, not 

one or both expression must be true for the overall expression to be true 

If intTemperature < 20 or intTemperature > 100 then

lblMessage.Text = "Unsafe temperature"

End if 

*Exclusive or 

*One but not both expressions must be true for overall expression to be true 

*Takes a Boolean Expression and reverses its logical value

*If the expression is true, the not operator returns false, and if the expression is false, it returns true. 

Gives you the opposite 

*Best for checking a value inside a range of numbers 

If inx >= 20 ANd intX <=40 Then

lblMessage.Text = "The value is in the acceptable range."

End if 

*Best for checking if a value is outside a range of numbers

If intX <20 Or intX > 40 Then

lblMessage.Text = "The value is outside the acceptable range."

End if 

From highest to lowest 

1. not 

2. and 

3. or 

4.xor

*relational operators can be used to compare strings and string literals 

strName1 = "Mary"

strName2 = "Mark"

If strName1 = strName2 Then

lblMessage.Txt = "Name are the same" 

Else 

lblMessage.Text = "Names are not the same"

End if

If txtInput.Text = String.Empty Then

lblMessage.Text = "Please enter a value" 

Else......

*Converts string to upper or lower case letters 

ToUpper

strLastName = txtLastName.Text.ToUpper()

ToLower

strBigTown = "NewYork"

strLittleTown = strBigTown.ToLower()

If txtInput.Text.Length >20 Then

lblMessage.Text = "Please enter no more than 20 characters."

End if 

TrimStart - returns the string with leading spaces removed 

TrimEnd - returns the string with trailing spaces removed

Trim - returns the string with leading and trailing spaces removed 

lblMessage1.Text = strGreeting.TrimStart()

*Returns a portion of a string 

StringExpression.Substring(StartPos)

strFullName = "George Washington"

strLastName = strFullName.Substring(7) "Washington"

strFullName = "George Washington"

strFirstName= strFullName.Substring (0,6) 

'   George 

*Searches for a specific string within a string 

*Returns the position of the first occurrence of SearchString within StringExpression, or -1 if SearchString is not found

IndexOf

IndexOfstrFullName = "George Washington"

intPosition = strFullName.IndexOf("Wash,9) 

strNumber = "567"

If IsNumeric (strNumber) Then 'returns true

strNumber = "567abc"

If IsNumeric(strNumber) Then 'returns false 

*Property is accessed via the dot operator 

strLastName.Length

*Method is accessed via the dot operator 

strLastName.ToLower()

*No dot operator when calling a function

IsNumeric (strLastName)

*One of several possible actions is taken, depending on the value of an expression

Select Case CInt(txtInput.Text)

Case 1

MessageBox.Show ("Day 1 is Monday")

Case 2

MessageBox.Show("Day 2 is tuesday)

OR

If CInt(txtInput.Text) = 1 Then

MessageBox.Show ("Day 1 is Monday")

If CInt(txtInput.Text) = 2 Then

MessageBox.Show("Day 2 is tuesday)

*When you're testing multiple possbile alues of an expression you would use select case

If intApplicantAge<16 Then

MessageBox.Show("Applicant is too young"

Elseif strApplicantCounty<> Watuauga" Then

MessageBox.Show("Applicant must live in Watuagua")

*Method converts the string representation of a value to a specific data type. A return value indicates whether the conversion succeeded:

returns true if it was successful

false is failed 

*Type.TryPasre(source, destination)

If Integer.TryParse(txtInput.Text, intNumber) Then

lblResult.Text = "Conversion Successful"

* is the process of inspecting user input to see whether it meets certain rules 

*Provides a quick and siple way to ask the user to enter data 

*Should not be used as a primary method of input

Dim strUserName As String

strUserName = InputBox("Enter you name")

okay will return value

cancel with return empty string

*Controls displays a list of items and also allows the user to select one or more items from the list.

*Displays a scroll bar when all items cannot be shown

*Use lst prefix when naming a list box

*Items = entries in a list box are stored in a property name

*Collection = items is a special type of property

Items Collection

ListBox.Items.Insert.(Index,Item)

*Items.Count = returns the number of items

*Items.Add() - adds an item at the end

*Items.Insert() - adds an items at specific position

*Items.Clear() - removes all items

*Items.Remove() removes specificed item

*Items.RemoveAt() removes at specificed index

*Items.Contains() - returns true if the collection contains the specified item, or false is if doesnt

If lstDogs.SelectedItem = "Boxer" Then

MessageBox.Show("You picked Boxer")

Else MessageBox.Show ("You chose another breed)

End if 

If lstDogs.SelectedIndex = -1 Then

MessageBox.Show ("no item is selected")

end if 

*A boolean property

*When set to true values in the item property are displayed in aplhabetical order

*When set to false, values in the items property are displayed in the order they were added

*Set to false by default 

*Repetition structure or loop causes one or more statements to repeat

*Each reprtition of the loop is = iteration

Three types:

1.do while

2.do until

3.for next

**A boolean expression that is tested for a true or false value

*a statement or group of statements that is repeated as long as the boolean expression is true 

Dim intCount As Integer = 0

Do While intCount <10

lstOutput.Items.Add ("Hello")

intCount += 1

Loop

*A loop must have some way to end itself

*If the test expression can never be false, the loop will continue to repeart forever

*A variable that is incremented or decremented in each loop interation

* Increment means add 1

*Decrement means to subtract 1

*Iterates until the expression is true

* Loop the expression is tested before the body is executed

Do While intCount<10

lstOutput.Items.Add("hello")

intCount += 1

Loop

*Loop the body is executed before expression is tested 

Do

lstOutput.Items.Add("Hello")

intCount += 1

Loop while intCount <10

*Ideal for loops that require a counter 

*Pretest form only

For intCount = 0 to 9

lstOutput.Items.Add ("Hello")

Next

Step Value 

*Is the value added to the counter variable at the end of each iteration. If not specified it defaultss to 1

For inCount = 0 to 100 Step 10

MessageBox.Show(intCount.ToString())

Next

counts as 0,10,20,30,40....100

*Exit do : used in do while or do until

*Exit for : used in for next loops 

caution it can be difficult to debug

Dim strInput As String

Do Until strInput = "John"

strInput = InputBox("What is the password")

If strInput = " " Then

Exit Do

End If 

Loop 

*For ..Next = when the number or required iterations is known

*Do while = when you wish the loop to repeat as long as the test expression is true

*Do until = when you wish the loop to repeat as long as the test pression is false 

*Loop insidde another loop

For intSeconds = 0 to 59

lblSeconds.Text = intSeconds.ToString()

Next 

For intSeconds = 0 to 59

lblSeconds.Text = intSeoncds.ToString()

* Boolean property with default alue of false 

*If set to true, entries can appear side by side

CheckedListBox

clb

*Variation of the listbox contril with a checkbox beside each item

*Determines how items may be checked.

False = user clickess item once to select it again to check it

True - user clicks item only once to both selet it and check it 

Dim intIndex As Integer

For inIndex = 0 To clbToppings.Items.Count - 1

If clbToppings.GetItemChecked (intIndex) Then

MessageBox.Show(clbToppings.Items (intIndex) + " is checked"

End if 

Next

*Method to set the checked state of each item in code. 

Dim intIndex As Integer

For intIndex = 0 To clbToppings.Items.Count - 1

clbToppings.SetItemChecked (intIndex, False)

Next 

ComboBox Control

cbo

*A cobination of a ListBox and a TextBox

*You can allow the user to either choose an item from the list or type in a value 

*Simple = visible, editable, type in a value and not limited to selecting what is there

*DropDown = click down arrow, editable

DropDownList = click down arrow, not editable

*Random.Net get a random integer nuber in the range minValue to maxValue

intNum= rand.Next (0,100) 

With textName

.clear()

.ForeColor = Color.Blue

.BackColor = Color.Yellow

End With

*Appears in the compnent tray, not the form

*Resizable region at the bottom of the designer window that holds invisible controls 

*AutoPopDelay = determines how long a tip is displayed

*InitialDelay = regulates the delay before a tip appears

*ReshowDelay = determines the time between the display of different tips as the user moves the mouse from control to control

*AutomaticDelay = sets the above 3 properties alll at once

*Payment returns the periodic payment amount for a loan with a fixed interest rate 

dblPayment = Pmt(dblAnnInt / 12, Number of Periods, loan amount which must be negative)

3 parts 

*Function returns the interest portion for a specific period of a loan with a fixed interest rate and fixed monthly payment

IPmt (PeriodsInterestRate, 12, Number of periods, -loan amount)

4 parts 

*Funcion returns the principal portion for a specific period of a loan with a fixed interest rate and fixed monthly payments

dblPrincipal = PPmt (dblAnnInt /12, Number of periods, -loan amount)

4 parts 

*The sume of the interest portion and principal portion will equal the total payment :

total payment = (interest portion)+(principal portion)