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ics151-hour05

 ics151-hour05

William Albritton

January 08, 2016
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  1. Instructor: William McDaniel Albritton Slides based on Sams Teach Yourself

    ASP.NET 4 in 24 Hours, Complete Starter Kit by Scott Mitchell
  2. Programming Languages  Programming languages use simple instructions to solve

    a specific problem  Such as calculating the monthly payments of a fixed- rate mortgage  Or displaying the current time and date
  3. Common Features  All programming languages have the following in

    common: 1. Use variables to temporarily store data 2. Use operators to manipulate the data stored in variables, such as adding (+) two variables 3. Use control structures, such as if statements and loops, to change the flow of the program 4. Use subroutines (functions, methods) to group together similar instructions of the program
  4. Variables  A variable is a place in the computer’s

    memory (RAM – random access memory), where you can store data, such as a number or string
  5. String Data Type  A String data type is a

    sequence of characters (letters, digits, and other keyboard characters), surrounded by double quotes (")  Such as "Hey, y'all!"  "Aloha" is a String  "The quick brown fox jumped over the lazy dog." is a String
  6. Variables  Variables have 3 components 1. Variables have a

    name, which is used to identify the value, such as Number5, PriceOfGas, or LastWords 2. Variables have a data type, which is used to restrict the kind of data that can be stored, such as Integer, Decimal, or String 3. Variables have a value, which is some sort of data, such as 5, 4.99, or "Hey man, check this out!"
  7. Variables as boxes  You should think of a variable

    as a box with a name that can only store values (data) of a certain data type name: LastWords data type: String value: "Hey man, check this out!"
  8. Variable Names  Visual Basic has a few restrictions on

    variable names 1. Two different variables cannot share the same name 2. Variable names cannot start with a number, so 5Num, 88, or 123abc are not valid names 3. Variable names are not case sensitive (uppercase and lowercase letters are the same), so NumberFive, numberFive, and numberfive are the same variable
  9. Initializing a Variable  Initialization is when you assign a

    name, data type, and value to a variable in one statement  Example initialization statements for Strings:  Dim Movie As String = "Shaw Shank Redemption"  Dim Name As String = "Sally Suzuki"  Dim LastWords As String = "Hey man, check this out!"  Syntax of initialization (Dim is short for dimension):  Dim Name As DataType = Value
  10. Two Parts  Initialization actually has two parts: 1. Declaration

    makes space in memory for the variable (makes a box) and assigns a name and data type to this space (write name and data type on box)  Example declaration statements:  Dim Number5 As Integer  Dim PriceOfGas As Decimal  Dim LastWords As String
  11. Two Parts  Initialization actually has two parts: 2. Assignment

    gives a value to a variable (puts a value in the box) by using the assignment operator, which is the equals sign (=)  Example assignment statements:  Number5 = 5  PriceOfGas = 4.99  LastWords = "hey man, check this out!"  The assignment operator (=) assigns the value on the right to the variable on the left
  12. Rules for Variable Creation  You can only create (initialize

    or declare) a variable one time  You have to create (initialize or declare) a variable before you use it in a method  Usually, you create variables at the beginning of your method  You cannot have two (or more) variables with the same name
  13. Comments  The apostrophe (') is used to make a

    comment in Visual Basic that people can read, but the computer cannot read  For example: 'Hey, Computer! 'Your cannot read this! 'Ha! Ha! Ha! 'Comments tell us humans how the code works
  14. String Operator  For Strings, we have the string concatenation

    operator (&), which attaches the end of the first string to the beginning of the second string  We have to put an & (ampersand) between every String  Examples:  Dim Word1 As String = "I " & "like"  Dim Word2 As String = "ice" & " " & "cream"  Dim Sentence As String = Word1 & " " & Word2 & "!"
  15. String Operator  A common mistake is to forget to

    begin or end the String with a double-quote  Examples of INCORRECT Strings:  Dim Word1 As String = "I " & like"  Dim Word2 As String = "ice" & " " & "cream  Dim Sentence As String = Word1 & " & Word2 & !"
  16. String Operator  Another common mistake is to forget to

    put a & between each String  Examples of INCORRECT Strings:  Dim Word1 As String = "I " "like"  Dim Word2 As String = "ice" & " " "cream"  Dim Sentence As String = Word1 & " " & Word2 "!"
  17. String Operator  See the class web page for code

    examples StringExample.aspx and StringExample.aspx.vp, which demonstrate initializing (creating) and concatenating (adding) strings  You have to create a web site in Visual Basic, and then a Web Form with the name StringExample and copy & paste the source code into the .aspx and .aspx.vb files to get this to work
  18. Tips: Naming Your File  Do not rename your file

     When you first create a file, decide on the name, and don’t change it  Otherwise, you will have to change the text in the .aspx and .vb files in at least three places
  19. Tips: Naming Your Variables  The variables in the .vb

    file should have different names than the Web Controls in the .aspx file  See the next slide for an example
  20. Tips: Naming  Example .aspx file HTML code: <asp:TextBox ID="Input"

    runat="server"> </asp:TextBox> <asp:Label ID="Output" runat="server"> </asp:Label>  Example .vb file Visual Basic code: Dim WordFromUser As String = Input.Text Dim Input As String = Input.Text Dim ThreeStrings As String = WordFromUser & " " & WordFromUser & " " & WordFromUser Output.Text = ThreeStrings
  21. Tips: Subroutines  These subroutines are in the .vb file

     Subroutines contain code that processes data  Usually there is an input, some processing, and an output  There are two subroutines that we will use: 1. Page_Load 2. Button_Click
  22. Tips: Subroutine Page_Load  This subroutine runs when the webpage

    is loaded into the browser  There is no input for this subroutine  The output for the subroutine is sent to the Label Web Control (from the Toolbox)  To create this subroutine: open the .vb file, click somewhere inside the class, on the left drop-down menu click: (Page Events), on the right drop-down menu click: Load
  23. Tips: Subroutines Button_Click  This subroutine runs when the user

    clicks on a button  The input for this subroutine is from a TextBox Web Control (from the Toolbox)  The output for the subroutine is sent to the Label Web Control (from the Toolbox)  To create this subroutine: open the .aspx file, add a button, change to the Design view, double click on the button, which will automatically open the .vb file and create the subroutine
  24. Tips: TextBox Web Control  The TextBox Web Control is

    used to input data from a webpage to the Button_Click subroutine  To simplify and clarify your code, you can change the ID="TextBox1" to ID="Input"  Default code: <asp:TextBox ID="TextBox1" runat="server"> </asp:TextBox>  More better code: <asp:TextBox ID="Input" runat="server"> </asp:TextBox>
  25. Tips: Label Web Control  The Label Web Control is

    used to display data output from a subroutine  We will always delete the Text="Label" attribute/value pair, because a value will be assigned in the .vb file  To simplify and clarify your code, you can change the ID="Label1" to ID="Output"  Default code: <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>  More better code: <asp:Label ID="Output" runat="server"> </asp:Label>
  26. Tips: <label> Element Bug  When you delete the Text="Label"

    attribute/value pair, don’t delete the last > (greater-than sign), or the Visual Basic code that corresponds to the <label> element will not be able to identify the label’s ID  Correct code: <asp:Label ID="Label1 " runat="server"></asp:Label>  Incorrect code: <asp:Label ID="Label1" runat="server"</asp:Label>
  27. Methods and Variables  Note that variables are only visible

    (can be used) within one method  Variables in one method are not visible (cannot be used) in a second method  See Methods.aspx and Methods.aspx.vb files for an example
  28. Integer Data Type  The Integer data type is a

    whole number (not a fraction or a decimal), which is roughly in the range -2 billion to 2 billion  Integer examples are 5, -5, 983254, etc.
  29. Initializing a Variable  Initialization is when you assign a

    name, data type, and value to a variable in one statement  Example initialization statements for Integers:  Dim Number5 As Integer = 5  Dim BigNumber As Integer = 2000000000  Dim NegativeNumber As Integer = -395  Syntax of initialization (Dim is short for dimension):  Dim Name As DataType = Value
  30. Variables as boxes  You should think of a variable

    as a box with a name that can only store values (data) of a certain data type name: Number5 data type: Integer value: 5
  31. Arithmetic Operators  For Integers (and Decimals), we can use

    these four binary operators (binary just means “2”): 1. Addition (+) 2. Subtraction (-) 3. Multiplication (*) 4. Division (/)
  32. Integer Division  Addition, subtraction, and multiplication work as usual,

    but Integer division will cut off the decimal point  will round up if greater than .5  will round up if x is odd for x.5 (if the number in front of .5 is an odd number)  will round down if x is even for x.5 (if the number in front of .5 is an even number)  will round down if less than .5
  33. Integer Division  For example:  10/6 is 2 (1.66666667

    – round up)  11/7 is 2 (1.57142857 – round up)  3/2 = 2 (1.5 – round up)  7/2 = 4 (3.5 – round up)  10/3 is 3 (3.33333333 – round down)  10/9 is 1 (1.111111111 – round down)  1/2 is 0 (0.5 – round down)  5/2 = 2 (2.5 – round down)
  34. Arithmetic Operators  For Integers (and Decimals), we can use

    the unary minus operator (unary just means “1”), which changes the variable to the opposite value 1.Unary minus operator (-)  Examples:  -(2) is -2  -(-5) is 5
  35. Arithmetic Operators  For Integers (and Decimals), we can use

    parenthesis to determine the order of operations  For example:  2+3*4 is 14 (because 3*4 is 12, and 2+12 is 14)  (2+3)*4 is 20 (because 2+3 is 5, and 5*4 is 20)
  36. Variable Names  Visual Basic has a few restrictions on

    variable names 1. Two different variables cannot share the same name 2. Variable names cannot start with a number, so 5Num, 88, or 123abc are not valid names 3. Variable names are not case sensitive (uppercase and lowercase letters are the same), so NumberFive, numberFive, and numberfive are the same variable
  37. Integer Examples  For some examples of Integer operators in

    action, see the web page IntegerExample.aspx and the Visual Basic file IntegerExample.aspx.vb  Try different values and see the results!  To view the examples, you have to make a web site, make a file with the name IntegerExample, copy and paste the source code into your files in Visual Web Developer
  38. Troubleshooting  Visual Basic code must go inside a method

     Good Visual Basic code: Partial Class IntegerExample Inherits System.Web.UI.Page Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click Dim Number1 As Integer = Input1.Text Dim Number2 As Integer = Input2.Text Dim Sum As Integer = Number1 + Number2 Output.Text = "The sum is " & Sum End Sub End Class
  39. Troubleshooting  If you do not have a method (event

    handler) for your button click or page load, then your Visual Basic program will not work  Bad Visual Basic code: Partial Class IntegerExample Inherits System.Web.UI.Page Dim Number1 As Integer = Input1.Text Dim Number2 As Integer = Input2.Text Dim Sum As Integer = Number1 + Number2 Output.Text = "The sum is " & Sum End Class
  40. Troubleshooting  Make sure you have the correct method 

    This is the Page_Load method, which does NOT get input from the user, because it runs automatically when the browser loads the webpage  Good Visual Basic code: Partial Class IntegerExample Inherits System.Web.UI.Page Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim Number1 As Integer = 5 Dim Number2 As Integer = 10 Dim Sum As Integer = Number1 + Number2 Output.Text = "The sum is " & Sum End Sub End Class
  41. Troubleshooting  This is the Button_Click method, which gets input

    from the user  Good Visual Basic code: Partial Class IntegerExample Inherits System.Web.UI.Page Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click Dim Number1 As Integer = Input1.Text Dim Number2 As Integer = Input2.Text Dim Sum As Integer = Number1 + Number2 Output.Text = "The sum is " & Sum End Sub End Class
  42. Troubleshooting  The HTML file and Visual Basic file communicate

    (send values) through the Text attribute of elements, so the value of the ID attribute for these elements must be the same in both files  Good code for File.aspx: <asp:TextBox ID="Input1" runat="server"></asp:TextBox>  Good code for File.aspx.vb: Dim Integer1 As Integer = Input1.Text
  43. Troubleshooting  If the value of the ID attribute is

    not the same in the HTML and Visual Basic files, your program will not work  Bad code for File.aspx: <asp:TextBox ID="Input1" runat="server"></asp:TextBox>  Bad code for File.aspx.vb: Dim Integer1 As Integer = Month.Text
  44. Troubleshooting  On the other hand, the name of the

    variable should be different than the value of the ID attribute  Good code for File.aspx: <asp:TextBox ID="Number1" runat="server"></asp:TextBox>  Good code for File.aspx.vb: Dim Integer1 As Integer = Number1.Text
  45. Troubleshooting  The program runs, but the computer gets confused

    if you use the same name for the variable and the value of the ID attribute  Bad code for File.aspx: <asp:TextBox ID="Number1" runat="server"></asp:TextBox>  Bad code for File.aspx.vb: Dim Number1 As Integer = Number1.Text
  46. Integer Exercise  See the class web page for an

    exercise using the Integer data type
  47. Decimal Data Type  A Decimal data type is a

    decimal number roughly in the range from -79 x 1027 to 79 x 1027  Example Decimals are 3.14, -5.0, and 987.324
  48. Common Features  All programming languages have the following in

    common: 1. Use variables to temporarily store data 2. Use operators to manipulate the data stored in variables, such as adding (+) two variables 3. Use control structures, such as if statements and loops, to change the flow of the program 4. Use subroutines and functions to group similar instructions of the program
  49. Variables  A variable is a place in the computer’s

    memory (RAM – random access memory), where you can store data, such as a number or string
  50. Data Types  Data types are used to restrict the

    kind of data that can be stored in a variable  Visual Basic is a strongly typed language  This means that once a variable is declared to be of a certain type, only values of this type can be assigned to this variable  Loosely typed languages use variables that can be assigned to any type
  51. Data Types  Once we declare number5 to be type

    Integer:  Dim Number5 As Integer = 5  Then we have to always assign Integers  Number5 = 129  We should not assign Number5 to a Decimal, as it will be automatically converted to an integer  Number5 = 99.99 (bad code)  We should not assign Number5 to a String, as it will crash your webpage  Number5 = "five funny frogs" (bad code)
  52. Data Types  There are many kinds of data types;

    however, for this class, we will only use these 3 data types: 1. String  Dim LastWords As String = "hey, check this out!" 2. Integer  Dim Number5 As Integer = 5 3. Decimal  Dim PriceOfGas As Decimal = 4.99
  53. Arithmetic Operators  For Decimals (and Integers), we can use

    these four binary operators (binary just means “2”): 1. Addition (+) 2. Subtraction (-) 3. Multiplication (*) 4. Division (/)
  54. The Division Operator  The result of a division operator

    (/) is always a Decimal  Even if the two operands are Integers, the result is still a Decimal number.  For example: Dim Y as Decimal = 3/2 'Y has value 1.5  If the result is assigned to an Integer variable, the result is cast (changed to a different type) into an Integer value.  For example: Dim X As Integer = 3/2 'X has value 1  Therefore, when dividing numbers, it is best to simply keep all the variables as type Decimal
  55. The Division Operator  Examples  Dim Num1 As Decimal

    = 10/5 'Num1 is 2.0 (not 2)  Dim Num2 As Decimal = 10/3 'Num2 is 3.3333333 (not 3)  Dim Num3 As Decimal = 10.0/3.0 'Num3 is 3.3333333  Dim Num4 As Integer = 10/3 'Num4 is 3  Dim Num5 As Decimal = 10/3 'Num5 is 3.3333333  Dim Num6 As Integer = 10.0/3.0 'Num6 is 3
  56. Arithmetic Operators  For Decimals (and Integers), we can use

    the unary minus operator (unary just means “1”), which changes the variable to the opposite value 1.Unary minus operator (-)  Examples:  -(2.2) is -2.2  -(-5.5) is 5.5
  57. Arithmetic Operators  For Decimals (and Integers), we can use

    parenthesis to determine the order of operations  For example:  2.0+3.0*4.0 is 14.0  because 3.0*4.0 is 12.0, and 2.0+12.0 is 14.0  (2.0+3.0)*4.0 is 20.0  because 2.0 +3.0 is 5.0 , and 5.0 *4.0 is 20.0
  58. Decimal Example  See the class web page for an

    example with the Decimal data type  DecimalExample.aspx  DecimalExample.aspx.vb
  59. Decimal Exercise  See the class web page for an

    exercise using the Decimal data type