4/15/09 Notes

IT 230 -- 4/15/09

Review Questions

What is a reference variable?
Ans: A variable that contains a reference to or address of an object.
What does static mean? Give an example of a static property and a static method.
Ans: static means that the property or method is invoked by the class name, not an object. DateTime.Now is an example of a static property; int.Parse is an example of a static method.
What is the difference between these constructor calls?
Ans: The first noarg constructor call creates a Random object with a seed computed from the time of day clock on the computer. The second constructor call has an argument that is the seed for the random number generator. The second object will produce the same random numbers every time the application runs. The first object will produce different random numbers everytime the application runs.
What are the minimum and maximum random values that can be returned by these method calls. r is a reference variable for a random object.
Ans: (1) min value=0, max value=2147483647; (2) min value=0, max value=64, (3) min value=1, max value=9.
Give other ways of displaying the random numbers of Problem 4 on a web page.
Ans: Using a Literal control, using a TextBox control, using the <%= => delimiters.

Find the mistakes:

<!- ASP.Net file with many mistakes.
<%! Page %>

<script language=C#>
public void btnClickMe_Click(object sender, EventArgs e)
{   txtClicks.Text++;  }

<html xmlsn=http://www.w3.org/1999/xhtml>
<head>
<title>clickcounter2.aspx Example</title>
<link rep=stylesheet class=css/txt href=examples.css>
<body>
</head>
<h2>Find the Mistakes</h1>
<form id=frm Main runat=server
</form>
<p>Random Value: 
<asp:Literal ID=litValue Value=0 style=text-align:right></p>
</body>

Ans: Here is the corrected version:

<!-- ASP.Net file with many mistakes. -->
<%! Page Language=C# %>

<script runat=server>
public void btnClickMe_Click(object sender, EventArgs e)
{   
    int n = int.Parse(txtClicks.Text);  
    n++;
    txtClicks.Text = n.ToString( );
}

<html xmlns=http://www.w3.org/1999/xhtml>>
<head>
<title>clickcounter2.aspx Example</title>
<link rep=stylesheet class=css/txt href=examples.css>
</head>

<body>
<h2>Find the Mistakes</h2>
<form id=frmMain runat=server>

<p>Random Value: 
<asp:Literal ID=litValue Value=0 style=text-align:right></p>

<p> <asp:Button ID=btnClickMe Text=Click Me
        OnClick=btnClickMe_Click />

</form>
</body>
</html>

Structured Programming

Look at Structured Programming
Look at Examples 13 through 16.

HTML Controls

Some traditional HTML controls with source code:
1. Button:
  
  Source Code: <input id=btnPushMe class=button value=Push Me />
2. Text Box:
  
  Source Code: <input id=txtInput class=text value=Default String />
3. Radio Buttons: Female Male
  
  Source Code: <input class=radio id=radFemale name=gender />
4. Check Box: Anonymous Login
  
  Source Code: <input class=checkbox id=chkAnonymous value=a checked />
5. Drop Down Menu:
  
  Source Code:
  <select id=ddmMenuChoice>
  <option value=B>Beef</option>
  <option value=C>Chicken</option>
  <option value=V>Vegetarian</option>
  </select>
6. Submit Button:
  
  Source Code: <input id=btnSubmit class=button value=Push Me />
The values in HTML controls can be sent back to the server when a submit button is clicked.
See how to add HTML tags to a form using Visual Studio.

ASP.Net Web Controls

ASP.Net Server controls have the asp: prefix in its tag.
Example ASP.Net source code for Web control tags:
1. Button: <asp:Button ID=btnPushMe Text=Push Me />
2. TextBox: <asp:TextBox ID=txtInput Text=0 />
Use Visual Studio to place the following controls on a form:
Check out the source that is created by Visual Studio.
Look at Examples 22 through 28. They illustrate ASP.Net Web controls

Project 3

Work on Project 3.