CIS162AD

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CIS162AD

• Loops, Lists, Printing
• 10_loops.ppt

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Overview of Topics

• While Loop
• Do While Loop
• For Loop
• Pretest vs Posttest
• Nested Loops
• List and Combo Boxes
• Printing Controls

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Flowcharting

• A flowchart is a pictorial representation of an
  algorithm or logical steps.
• Each step is represented by a symbol and the
  arrows indicate the flow and order of the steps.
• The shape of the symbol indicates the type of
  operation that is to occur.
• Flowcharts may help the move visual students
  learn and understand logic.

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Flowchart Symbols
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Flow Control Structures

• The order in which statements are executed.
• There are four structures.
• Sequence Control Structure
• Selection Control Structure
• Also referred to as branching (if and if-else)
• Case Control Structure (select)
• Repetition Control Structure (loops)

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4. Repetition Control (loops)

• Loops are the 4th flow control structure.
• Loop a group of statements that are repeated
  until a certain condition occurs to stop it.
• The conditions are Boolean expressions like those
  in if statements.
• The conditions evaluate to True or False.
• Can use Relational and Logical Operators.

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While is a Pretest Loop - Example

• intCount 1 //initialize controlling variable
• while (intCount lt 4)
• txtCount.Text intCount.ToString(N0)
• intCount //add one
• Output
• 1 2 3 

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While is a Pretest Loop

• Pretest - controlling condition is evaluated
  before executing loop body.
• Controlling variable must be initialized.
• Condition must be true to enter loop body.
• There is NO semi-colon after the condition.
• It is possible that body is not executed at all.
• Condition must be false to get out of loop.
• Controlling variable should be modified within
  the loop.
• Execution continues with next statement after
  Loop.

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Flowchart While Pretest Loop
Initialization important for While Pretest Loop
count 1
while count lt 4
False
True
Output count
Skip or Exit Loop
Represents Loop
count 1
Next statement
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Do-While is a Posttest Loop -Example

• intCount 1 //initialize controlling variable
• do
• txtCount.Text intCount.ToString(N0)
• intCount
• while (intCount lt 4)
• Output
• 1 2 3 

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Do-While Posttest Loop

• Posttest - controlling condition is evaluated
  after executing loop body.
• So, body is always executed at least one time.
• Initialization of controlling variable not
  necessarily required.
• Condition must be false to get out of loop.
• There is a semi-colon after the condition.
• Controlling variable should be modified within
  the loop.
• Execution continues with next statement after
  Loop.

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Flowchart Do-While Posttest Loop
count 1
Output count
Loop will be executed at least one time, because
the condition is at the bottom.
count 1
Represents Loop
while count lt 4
True
False - Exit Loop
Next statement
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Pretest vs. Posttest

• Pretest
• For pretest loops the terminating condition is at
  the top of the loop.
• It is possible that the body is not executed if
  the condition to get into the loop is not met.
• Posttest
• For posttest loops the terminating condition is
  at the bottom of the loop.
• The body is always executed at least one time.

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Loop Summary

• Infinite loop
• A loop that never ends.
• While condition always evaluates to true.
• Controlling variable must be altered within the
  loop.
• Click on the close form icon to stop the program.
• Use Control-Break to enter debug mode.
• When to use a While or Do-While will become
  evident as we continue to use and learn each
  loop.
• Nested Loop is a loop inside another loop (see
  next slide).

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Nested Loops
1
1 2 3
2
1 2 3

• intCount 1
• while (intCount lt 4)
• txtCount.Text intCount.ToString(N0)
• intCount
• intCount2 1
• do
• txtCount.Text intCount2.ToString(N0)
• intCount2
• while (intCount2 lt 4)

3
1 2 3
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For Loop

• Good when a task needs to be completed a fixed
  number of times.
• Good when counting with fixed increments.
• Compares to a While Pretest loop.for
  (initialization condition action) body

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For Loop

• //For includes initialization and ending
  condition
• for (int intCount 1 intCount lt 4 intCount)
• txtCount.Text intCount.ToString(N0)
• Output
• 1 2 3

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For Loop

• Controlling variable is initialized.
• Pretest - controlling condition is evaluated
  before executing loop body.
• Condition must be true to enter loop body.
• It is possible that body is not executed at all.
• Condition must be false to get out of loop.
• The action (intCount) is automatically executed
  when the bottom of the loop is reached, and then
  the condition is evaluated again.
• Do not alter the value of controlling variable
  within the body.
• Compares to a While Pretest loop.

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Flowchart For Pretest Loop
count 1
while count lt 4
False
True
Output count
Skip or Exit Loop
Represents Loop
count 1
Next statement
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Nested For-Next Loops

• For loops may contain other For loops.
• The second loop must be completely contained
  inside the first loop.
• The second loop should have a different
  controlling variable.
• Should indent inner loops for readability.

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Nested For-Next Layout

• for (i 1 i lt 10 i)
• for (j 1 j lt 20 j) for (k 1 k lt
  15 k) //body

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List and Combo Boxes
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List and Combo Boxes

• Both allow you to have a list of items from which
  the user can make a selection.
• Items in the list can be set at design time or
  loaded at run-time.
• Space on the form and input options will help
  determine which to use.
• A scroll bar automatically added for long lists.
• Since the two are similar, well only review the
  combo boxes here.
• See textbook additional options and details.

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Collection of items

• The list of items that is displayed is called a
  collection.
• A collection is an object that has properties and
  methods.
• Properties item count, selected index
• Methods add, remove, clear
• Each item in the list is referred to an element.
• Each element is referenced by providing an index
  value.
• The first one is referenced with an index value
  of zero.

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Design Time Use Items Property

• In the properties window there is a property
  named Items.
• Use the Collection Editor button to open a window
  that allows you to enter the items.
• One item per line (cboCatalog example) Odds and
  Ends Solutions Camping Needs

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Collection Concepts
Position Index Text
1 0 Odds and Ends
2 1 Solutions
3 2 Camping Needs
There are 3 items. The first is referenced with
an index value of zero. The last one is
referenced with an index value of Items.Count
1 The item the user picks is recorded in
SelectedIndex.
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Run Time methods

• To add an item to the end of the list at run time
  use the Items.Add method. cboCatalog.Items.Add(T
  oolTime) cboCatalog.Items.Add(Spiegel)
• To insert an item in a particular place in the
  list use Items.Insert. cboCatalog.Items.Insert(1,
  The Outlet)
• Use the cboCatalog.Items.RemoveAt(index) or
  cboCatalog.Items.Remove(strValue) to remove items
  from list.
• Use cboCatalog.Items.Clear( ) to remove all items
  in the list.

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Selected Item

• When we are ready to process the form, well want
  to record the item the user selected.
• The SelectedIndex can be usedstrCatalog
  cboCatalog.Items(cboCatalog.SelectedIndex)
• The Text property also holds the text of the
  selected item.strCatalog cboCatalog.Text

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Printing Documents

• Printing documents is not as easy as creating
  forms.
• There are other tools that can be used to create
  reports, such as Crystal Reports.
• However, there will be times when information
  from an application may need to be printed.
• Use the PrintDocument control by adding it to the
  component tray.

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Print Page Event

• The PrintDocument control is named like other
  controls, such as printDocument1.
• Add a Print option using a button or menu item.
• From the button or menu click method, call the
  Print method. printDocument1.Print( )
• This will fire the PrintPage event.
• In the PrintPage event method is where we place
  the code to print a page.

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Graphics Page

• A graphics page is built in memory and then the
  page is sent to the printer.
• You must specify the exact location on the
  graphics page for each element that you want to
  print.
• There are various methods to draw on the graphics
  page, but well just cover the introductory ones
  here.

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X and Y Coordinates
X
Y
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e.Graphics.DrawString Method

• Use the DrawString method to send a line of text
  to the graphics page.
• Pass the upper-left corner of where you want the
  string placed as X and Y coordinates.
• e.Graphics.DrawString(strToPrint, Font, Brush, X,
  Y)
• Font can be specified
• Brush is the color

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PrintPage Event Logic

• Declare coordinate, line height and font
  variables.
• float fltX, fltY, fltLineHeight
• Font printFont new Font(Arial, 12)
• Get left margin and top margin values using some
  of the properties of the page event.
• fltX e.MarginBounds.Left
• fltY e.MarginBounds.Top
• Call DrawString to place a line on the graphics
  page.
• Move down the page by increasing Y.Assign the
  font height to line height. fltLineHeight
  printFont.GetHeight( )Add the height of the
  line just printed to Y. fltY fltLineHeight
• When the procedure is exited, the graphics page
  is sent to the printer.

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Print Preview

• Place a PrintPreviewDialog control in the
  component tray.
• The control is named printPreviewDialog1.
• Add a menu or button control for the user to
  select, and for its event use the
  code printPreviewDialog1.Document
  printDocument1 printPreviewDialog1.ShowDialog(
  )
• Use the same PrintDocument control declared for
  the printer output.
• Assign the PrintDocument to the Document property
  of the printPreviewDialog1 and call ShowDialog.
• ShowDialog will fire the PrintPage event, so the
  same code to create the page is executed for
  print preview and an actual print.

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Summary

• While Loop
• Do While Loop
• For Loop
• Pretest vs Posttest
• Nested Loops
• List and Combo Boxes
• Printing Controls
• I may have over simplified the Print process in
  this presentation. The best way to learn it is
  to practice it (CS10).