Lecture5

• ListBox


  A control that displays a list of items that the user can select from
• ListBox


  • Has various methods and properties that you can use in code to manipulate the ListBox's contents
  • The Items.Add method allows you to add an item to the ListBox control
  • The Items.Clear method can erase all the items in the Items property
  • The Count property reports the number of items stored in the ListBox
• Sample Codes


  • You can add string literals
  • You can add values of other types as well
• while loop


  Causes a statement or set of statements to repeat as long as a Boolean expression is true
• Structure of a while Loop

  1. Boolean expression that is tested for a true or false value

  2. Statement or set of statements that is repeated a long as the Boolean expression is true
• while Loop


  • It is a pretest loop, testing its condition before performing an iteration
  • Requires a counter variable with initial value to be declared, so the Boolean expression can be tested
• Sample Code (1 of 4)


  • The counter has an initial value of 1
  • Each time the loop executes, 1 is added to counter
  • The Boolean expression will test whether counter is less than or equal 5. So the loop will stop when counter equals 5
• Infinite Loop


  A loop that will repeat until the program is interrupted, typically caused by the programmer forgetting to write code that makes the test condition false
• Increment


  To increase the value of a variable
• Decrement


  To decrease the value of a variable
• Postfix Mode


  Placing the ++ and -- operators after their operands
• Prefix Mode


  Placing the ++ and -- operators before their operands
• for Loop


  A loop that is specially designed for situations requiring a counter variable to control the number of times that a loop iterates
• Structure of a for Loop

  1. Initialization: a one-time expression that defines the initial value of the counter

  2. Test: A Boolean expression to be tested. If true, the loop iterates.

  3. Update: increase or decrease the value of the counter
• Sample Code (2 of 4)

  • The initialization expression assigns 1 to the count variable
  • The expression count <=5 is tested. If true, continue to display the message.
  • The update expression adds 1 to the count variable
• do-while Loop


  A posttest loop, which means it performs an iteration before testing its Boolean expression
• Sample Code

  • Will you see the message box?
• Text File


  Contains data that has been encoded as test using a scheme such as Unicode
• Binary File


  Contains data that has not been converted to text. You cannot view the contents of binary files with a text editor.
• StreamWriter


  A class for writing data to a text file
• StreamReader


  A class for reading data from a text file
• Writing Data to a File

  1. Create a StreamWriter object

  2. Use one of the File methods to open the file to write to

  3. Use the Write or WriteLine method to write items of data to the file

  4. Close the connection
• CreateText


  A File method that creates a text file, erasing any existing contents
• AppendText


  A File method that opens a text file for appending, without erasing any existing contents
• Reading Data from a File

  1. Create a StreamReader object

  2. Use the File.OpenText method to open the file to read from

  3. Use the Read or ReadLine method to read items of data from the file

  4. Close the connection
• OpenFileDialog


  A control that displays a standard Windows Open dialog box
• SaveFileDialog


  A control that displays a standard Windows Save As dialog box
• Displaying an Open Box

  1. Add the OpenFileDialog control to the form

  2. Call the ShowDialog method to display the Open dialog box
• DialogResult


  A value returned by the ShowDialog method indicating which button the user clicked to dismiss the dialog box
• Filename


  A property of the OpenFileDialog and SaveFileDialog controls that stores the path and filename of the selected file
• InitialDirectory


  A property of the OpenFileDialog and SaveFileDialog controls that specifies the directory to be initially displayed
• Random

  A class in the .NET Framework that generates random numbers
• Generating Random Numbers

  1. Create a Random object

  2. Use the Next method to generate a random integer

  3. Use the NextDouble method to generate a random floating-point number between 0.0 and 1.0
• Load Event


  An event that occurs when a form is loaded into memory
• ComboBox


  A control that combines a TextBox and a ListBox, allowing the user to either type in a value or select one from a list
• ComboBox vs ListBox


  • ComboBox is appropriate when there is a list of suggested choices (but the user can easily add/insert new items)
  • ListBox is appropriate when you want to limit input to what is on the list
• ComboBox DropDownStyle


  Simple, DropDown (default), DropDownList