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Introduction to Conditional Statements

  

if a Condition is true

A conditional statement is an expression that produces a true or false result. To create the expression, you use a Boolean operator and a logical keyword.

 

Practical LearningPractical Learning: Introducing Conditional Expressions

  1. Start Microsoft Visual Studio or Microsoft Visual Web Developer
  2. Start creating a web site
  3. Set the language to Visual C# et set the site name to timesheet1
  4. Click OK
  5. In the Solution Explorer, right-click Default.aspx and click Rename
  6. Type index.aspx and press Enter
  7. Click the Source button and change the file as follows:
     
    <%@ Page Language="C#"
             AutoEventWireup="true"  
             CodeFile="index.aspx.cs" 
             Inherits="_Default" %>
    
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head runat="server">
    <title>Time Sheet</title>
    </head>
    <body>
    <form id="frmTimeSheet" runat="server">
    <div>
        
    
    <table border="0" width="600">
      <tr>
        <td width="80"></td>
        <td align="center">Monday</td>
        <td align="center">Tuesday</td>
        <td align="center">Wednesday</td>
        <td align="center">Thursday</td>
        <td align="center">Friday</td>
        <td align="center">Saturday</td>
        <td align="center">Sunday</td>
      </tr>
      <tr>
        <td>Week 1:</td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Monday"
                         runat="server"
                         Columns="5">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Tuesday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Wednesday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Thursday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Friday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Saturday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek1Sunday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
      </tr>
      <tr>
        <td>Week 2:</td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Monday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Tuesday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Wednesday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Thursday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Friday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Saturday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
        <td align="center">
            <asp:TextBox ID="txtWeek2Sunday"
                         Columns="5" runat="server">0.00</asp:TextBox>
          </td>
      </tr>
    </table>
    
    &nbsp;
    <table width="600">
      <tr>
        <td align="center">
            <asp:Button ID="btnEvaluate" Width="200"
                        Text="Evaluate Time Sheet" runat="server" />
        </td>
      </tr>
    </table>
    &nbsp;
    
    <table border="0" width="300">
      <tr>
        <td width="33%"></td>
        <td align="center">Regular Time</td>
        <td align="center">Overtime</td>
      </tr>
      <tr>
        <td align="center">Week 1</td>
        <td width="33%" align="center">
            <asp:TextBox ID="txtWeek1RegularTime"
                         Columns="10" runat="server">0.00</asp:TextBox>
          </td>
        <td width="34%" align="center">
            <asp:TextBox ID="txtWeek1Overtime"
                         Columns="10" runat="server">0.00</asp:TextBox>
          </td>
      </tr>
      <tr>
        <td width="33%" align="center">Week 2</td>
        <td width="33%" align="center">
            <asp:TextBox ID="txtWeek2RegularTime"
                         Columns="10" runat="server">0.00</asp:TextBox>
          </td>
        <td width="34%" align="center">
            <asp:TextBox ID="txtWeek2Overtime"
                         Columns="10" runat="server">0.00</asp:TextBox>
          </td>
      </tr>
    </table>
    
    </div>
    </form>
    
    </body>
    </html>
  8. Save the file and click the Design button

if

Consider the following code:

<%@ Page Language="C#" %>
<html>
<head>

<script runat="server">

private void IndexHouseSelected(object sender, EventArgs e)
{
    lblSelection.Text = TypesOfHouses.Text;
}
</script>

<title>Altair Real Estate</title>
</head>
<body>

<h3>Altair Real Estate</h3>

<form id="frmRealEstate" method="post" runat="server">
  <table>
    <tr>
      <td>What type of property do you want to purchase?</td>
      <td>
	<asp:DropDownList id="TypesOfHouses"
			  AutoPostBack="True"
     OnSelectedIndexChanged="IndexHouseSelected" runat="server">
    	  <asp:ListItem>Condominium</asp:ListItem>
    	  <asp:ListItem>Townhouse</asp:ListItem>
    	  <asp:ListItem>Single Family</asp:ListItem>
    	  <asp:ListItem>Unknown</asp:ListItem>
  	</asp:DropDownList>
      </td>
    </tr>
    <tr>
      <td colspan="2">
	<asp:Label id="lblSelection" runat="server"></asp:Label></td>
    </tr>
  </table>
</form>

</body>
</html>

Here is an example of using it:

Conditions

To check if an expression is true and use its Boolean result, you can use the if operator. Its formula is:

if(Condition) Statement;

The Condition can be a type of Boolean operation. That is, it can have the following formula:

Operand1 BooleanOperator Operand2

If the Condition produces a true result, then the Statement is executed. If the statement to execute is short, you can write it on the same line with the condition that is being checked. Here is an example:

<%@ Page Language="C#" %>
<html>
<head>

<script runat="server">

private void IndexHouseSelected(object sender, EventArgs e)
{
    int choice = TypesOfHouses.SelectedIndex;
    string description = "Unknow means the property cannot be clearly described";

    if( choice == 3 ) lblSelection.Text = description;
}
</script>

<title>Altair Real Estate</title>
</head>
<body>

<h3>Altair Real Estate</h3>

<form id="frmRealEstate" method="post" runat="server">
  <table>
    <tr>
      <td>What type of property do you want to purchase?</td>
      <td>
	<asp:DropDownList id="TypesOfHouses"
			  AutoPostBack="True"
     OnSelectedIndexChanged="IndexHouseSelected" runat="server">
    	  <asp:ListItem>Condominium</asp:ListItem>
    	  <asp:ListItem>Townhouse</asp:ListItem>
    	  <asp:ListItem>Single Family</asp:ListItem>
    	  <asp:ListItem>Unknown</asp:ListItem>
  	</asp:DropDownList>
      </td>
    </tr>
    <tr>
      <td colspan="2">
	<asp:Label id="lblSelection" runat="server"></asp:Label></td>
    </tr>
  </table>
</form>

</body>
</html>

Here is an example of running the program:

Real Estate

If the Statement is too long, you can write it on a different line than the if condition. Here is an example:

<script runat="server">
private void IndexHouseSelected(object sender, EventArgs e)
{
    if( TypesOfHouses.SelectedIndex == 3 )
	lblSelection.Text = "This property is not easily defined";
}
</script>

You can also write the Statement on its own line even if the statement is short enough to fit on the same line with the Condition.

Although the (simple) if statement is used to check one condition, it can lead to executing multiple dependent statements. If that is the case, enclose the group of statements between an opening curly bracket “{“ and a closing curly bracket “}”. Here is an example:

<script runat="server">
private void IndexHouseSelected(object sender, EventArgs e)
{
    string description = "";

    if( TypesOfHouses.SelectedIndex == 3 )
    {
	description = "A property is marked as \"Unknown\" ";
	description = description + "if is neither a condo, ";
	description = description + "a townhouse (or town home), ";
	description = description + "nor a single family.";
    }

    lblSelection.Text = description;
}
</script>

This would produce:

Real Estate

Here is another example of using it:

Real Estate

If you omit the brackets, only the statement that immediately follows the condition would be executed.

Just as you can write one if condition, you can write more than one. Here are examples:

<%@ Page Language="C#" %>
<html>
<head>

<script runat="server">
private void HouseSelected(object sender, EventArgs e)
{
    string description = "";
    
    if( TypesOfHouses.SelectedIndex == 0 )
	description = "A condominium is a sectional home " +
		"built as part of building. The building " +
		"would be made of one or more levels and " +
		"the condominiums are spread in different " +
		"parts. The building could be a simple " +
		"classic one or luxurious.";

    if( TypesOfHouses.SelectedIndex == 1 )
	description = "A townhouse, also called a town house, " +
		"or a townhome, or a town home is a house that " +
		"is attached to at least one other.";

    if( TypesOfHouses.SelectedIndex == 2 )
	description = "A single family is a house that stands " +
		"by itself. The house touches the floor and has " +
		"a roof. The house is not attached to any other " +
		"house. A single family can have one or more stories.";

    txtDescription.Text = description;
}
</script>

<title>Altair Real Estate</title>
</head>
<body>

<h3>Altair Real Estate</h3>

<form id="frmRealEstate" method="post" runat="server">
  <table>
    <tr>
      <td>What type of property do you want to purchase?</td>
      <td>
	<asp:DropDownList id="TypesOfHouses"
			  AutoPostBack="True"
     OnSelectedIndexChanged="HouseSelected" runat="server">
    	  <asp:ListItem>Condominium</asp:ListItem>
    	  <asp:ListItem>Townhouse</asp:ListItem>
    	  <asp:ListItem>Single Family</asp:ListItem>
    	  <asp:ListItem>Unknown</asp:ListItem>
  	</asp:DropDownList>
      </td>
    </tr>
  </table>

  <table>
    <tr>
      <td valign="top">Description:</td>
      <td>
	<asp:TextBox ID="txtDescription"
       		     TextMode="Multiline"
       		     Columns="40"
       		     Rows="3"
       		     runat="server"></asp:TextBox></td>
    </tr>
</form>

</body>
</html>

Here are examples of using the web page:

Real Estate

Real Estate

Real Estate 

 
 
 
 

if…else

If you use an if condition to perform an operation and if the result is true, we saw that you could execute the statement. Any other result would be ignored. To address an alternative to an if condition, you can use the else condition. The formula to follow is:

if(Condition)
    Statement1;
else
    Statement2;

Once again, the Condition can be a Boolean operation. If the Condition is true, then Statement1 would execute. If the Condition is false, then Statement2 would execute. Here is an example:

<%@ Page Language="C#" %>
<html>
<head>

<script runat="server">
private void btnValidateClick(object sender, EventArgs e)
{    
    if( CarGarage.Checked == true )
	lblDescription.Text = "We will look for a " +
		TypesOfHouses.Text + " with an indoor car garage.";
    else
	lblDescription.Text = "We have many " +
		TypesOfHouses.Text + "s without garages.";
}
</script>

<title>Altair Real Estate</title>
</head>
<body>

<h3>Altair Real Estate</h3>

<form id="frmRealEstate" runat="server">
  <table>
    <tr>
      <td>What type of property do you want to purchase?</td>
      <td>
	<asp:DropDownList id="TypesOfHouses" runat="server">
    	  <asp:ListItem>condominium</asp:ListItem>
    	  <asp:ListItem>townhouse</asp:ListItem>
    	  <asp:ListItem>single family</asp:ListItem>
  	</asp:DropDownList>
      </td>
    </tr>
    <tr>
      <td>Should the house have a car garage?</td>
      <td>
	<asp:CheckBox id="CarGarage" Checked="False" runat="server" />
      </td>
    </tr>
    <tr>
      <td colspan="2" align="right">
	<asp:Button id="btnValidate"
		    Text="Check Property Availability"
		    OnClick="btnValidateClick"
		    runat="server"></asp:Button>
      </td>
    </tr>
    <tr>
      <td colspan="2">
	<asp:Label id="lblDescription" runat="server"></asp:Label>
      </td>
    </tr>
</form>

</body>
</html>

Here is an example of using the web page:

Real Estate

Here is another selection made on the drop down list:

Real Estate

Practical LearningPractical Learning: Using the if...else Condition

  1. Double-click the Evaluate button
  2. To use the if...else condition, implement the event as follows:
     
    protected void btnEvaluate_Click(object sender, EventArgs e)
        {
            double Week1Monday, Week1Tuesday, Week1Wednesday,
                   Week1Thursday, Week1Friday, Week1Saturday, Week1Sunday;
            double Week2Monday, Week2Tuesday, Week2Wednesday,
                   Week2Thursday, Week2Friday, Week2Saturday, Week2Sunday;
            double Week1RegularTime, Week1Overtime,
                   Week2RegularTime, Week2Overtime;
            double Week1Total, Week2Total;
    
            Week1Monday = double.Parse(txtWeek1Monday.Text);
            Week1Tuesday = double.Parse(txtWeek1Tuesday.Text);
            Week1Wednesday = double.Parse(txtWeek1Wednesday.Text);
            Week1Thursday = double.Parse(txtWeek1Thursday.Text);
            Week1Friday = double.Parse(txtWeek1Friday.Text);
            Week1Saturday = double.Parse(txtWeek1Saturday.Text);
            Week1Sunday = double.Parse(txtWeek1Sunday.Text);
    
            Week2Monday = double.Parse(txtWeek2Monday.Text);
            Week2Tuesday = double.Parse(txtWeek2Tuesday.Text);
            Week2Wednesday = double.Parse(txtWeek2Wednesday.Text);
            Week2Thursday = double.Parse(txtWeek2Thursday.Text);
            Week2Friday = double.Parse(txtWeek2Friday.Text);
            Week2Saturday = double.Parse(txtWeek2Saturday.Text);
            Week2Sunday = double.Parse(txtWeek2Sunday.Text);
    
            Week1Total = Week1Monday + Week1Tuesday + Week1Wednesday +
                         Week1Thursday + Week1Friday +
                         Week1Saturday + Week1Sunday;
    
            if( Week1Total < 40 )
            {
                Week1RegularTime = Week1Total;
                Week1Overtime = 0;
            }
            else
            {
                Week1RegularTime = 40;
                Week1Overtime = Week1Total - Week1RegularTime;
            }
    
            Week2Total = Week2Monday + Week2Tuesday + Week2Wednesday +
                         Week2Thursday + Week2Friday +
                         Week2Saturday + Week2Sunday;
    
            if( Week2Total < 40 )
            {
                Week2RegularTime = Week2Total;
                Week2Overtime = 0;
            }
            else
            {
                Week2RegularTime = 40;
                Week2Overtime = Week2Total - Week2RegularTime;
            }
    
            txtWeek1Monday.Text = Week1Monday.ToString("F");
            txtWeek1Tuesday.Text = Week1Tuesday.ToString("F");
            txtWeek1Wednesday.Text = Week1Wednesday.ToString("F");
            txtWeek1Thursday.Text = Week1Thursday.ToString("F");
            txtWeek1Friday.Text = Week1Friday.ToString("F");
            txtWeek1Saturday.Text = Week1Saturday.ToString("F");
            txtWeek1Sunday.Text = Week1Sunday.ToString("F");
    
            txtWeek2Monday.Text = Week2Monday.ToString("F");
            txtWeek2Tuesday.Text = Week2Tuesday.ToString("F");
            txtWeek2Wednesday.Text = Week2Wednesday.ToString("F");
            txtWeek2Thursday.Text = Week2Thursday.ToString("F");
            txtWeek2Friday.Text = Week2Friday.ToString("F");
            txtWeek2Saturday.Text = Week2Saturday.ToString("F");
            txtWeek2Sunday.Text = Week2Sunday.ToString("F");
    
            txtWeek1RegularTime.Text = Week1RegularTime.ToString("F");
            txtWeek1Overtime.Text = Week1Overtime.ToString("F");
            txtWeek2RegularTime.Text = Week2RegularTime.ToString("F");
            txtWeek2Overtime.Text = Week2Overtime.ToString("F");
        }
    }
  3. Execute the application to test it
     
    Time Sheet
  4. Enter some values in the days text boxes. Here are examples:
     
    Time Sheet
  5. Click the Evaluate button
     
    Time Sheet
  6. Close the browser and return to your programming environment
 
 
   
 

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