The If Statement

Using relational operators,conditional expressions are set up to compare values and these operators, which were presented earlier, are repeated in the following table.

Operator	Use
=	Tests whether two values are equal.
<>	Tests whether two values are not equal.
<	Tests whether the first value is less than the second value.
>	Tests whether the first value is greater than the second value.
<=	Tests whether the first value is less than or equal to the second value.
>=	Tests whether the first value is greater than or equal to the second value.

A conditional expression is formed by relating values -- either constants or variables -- with these operators. The comparison is evaluated as Boolean True or False, and the script reacts to that condition. The following script presents a simple example of script decision making.

Sub Button_Click (Src As Object, Args As CommandEventArgs)

If Args.CommandName = "Button 1" Then

ButtonResponse.Text = "You clicked Button 1"

End If

End Sub

<asp:Button Text="Click Me" runat="server"
OnCommand="Button_Click" CommandName="Button 1"/>
<asp:Button Text="Click Me" runat="server"
OnCommand="Button_Click" CommandName="Button 2"/>
<asp:Label id="ButtonResponse" EnableViewState="False" runat="server"/>

Logical Operators

Sometimes you need to combine condition tests and that time, you might need to know if a numeric value is within a particular range; that is, whether the number is greater than one value and less than another value. Or, you might want to see if the number is outside a range by testing whether it is less than one value or greater than a second value and these kinds of combination tests are made possible by using two or more relational tests combined with the logical operators And, Or, and Not to form multiple comparisons. These operators were presented earlier and are repeated in the table given below.

Logical Operator	Comparison
And	condition1 And condition2 The condition1 and condition2 tests both must be true for the expression to be evaluated as True.
Or	condition1 Or condition2 Either the condition1 or condition2 test must be true for the expression to be evaluated as True.
Not	Not condition The expression result is set to its opposite; a True condition is set to False and a False condition is set to True.
Xor	condition1 Xor condition2 Either condition1 is true or condition2 is true, but not both, for the condition test to be evaluated as True.

Below is an example that uses a multiple condition test and after entering a value in the text box, click the "Check" button. The script determines if you entered a number between 1 and 10.If so, confirms this value with a message.

Sub Check_Number (Src As Object, Args As EventArgs)

If Number.Text <> "" Then

If Number.Text >= 1 And Number.Text <= 10 Then
NumberResponse.Text = "The number is between 1 and 10."
End If

End If

End Sub
<asp:TextBox id="Number" Size="1" runat="server"/>
<asp:Button Text="Check" OnClick="Check_Number" runat="server"/>
<asp:Label id="NumberResponse" EnableViewState="False" runat="server"/>

If Number.Text <> "" Then checks whether a value has been entered into the textbox (it is not equal to empty, or null) and if this condition is true, then the enclosed statements are executed. The enclosed statements form a second If test and in this case the value entered in the textbox is tested so see if it is greater than or equal to 1 and if it is less than or equal to 10. If these two conditions are true, then only the message is displayed

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