Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

use a single equals sign in C# unless you’re assigning a value to a variable; other-

wise your code will have a very different meaning than you expect!

Breaking Long Lines of Code

Since the message string in the above example was too long to fit on one line in

this book, we used the string concatenation operator to combine two shorter

strings on separate lines to form the complete message. In VB, we also had to

break one line of code into two using the line continuation symbol (_, an under-

score at the end of the line to be continued). Since C# marks the end of each

command with a semicolon (;), you can split a single command over two lines

in this language without having to do anything special.

We’ll use these techniques throughout this book to present long lines of code

within a limited page width. Feel free to recombine the lines in your own code

if you like—there's no length limit on lines of VB and C# code.

Conditional Logic

As you develop ASP.NET applications, there will be many instances in which

you’ll need to perform an action only if a certain condition is met, for instance,

if the user has checked a certain checkbox, selected a certain item from a

DropDownList control, or typed a certain string into a TextBox control. We check

for such occurrences using conditionals, the simplest of which is probably the If

statement. This statement is often used in conjunction with an Else statement,

which specifies what should happen if the condition is not met. So, for instance,

we may wish to check whether or not the name entered in a text box is Zak,

redirecting the user to a welcome page if it is, or to an error page if it’s not:

Visual Basic

If (userName.Text = "Zak") Then

Response.Redirect("ZaksPage.aspx")

Else

Response.Redirect("ErrorPage.aspx")

End If

C#

if (userName.Text == "Zak")

{

Response.Redirect("ZaksPage.aspx");

}

else

{

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Chapter 3: VB and C# Programming Basics

Response.Redirect("ErrorPage.aspx");

}

Take Care with Case Sensitivity

Instructions are case-sensitive in both C# and VB, so be sure to use if in

C# code, and If in VB code. On the other hand, variable and function

names are case-sensitive only in C#. As such, in C# you could have two

variables called x and X, which would be considered to be different; in VB,

they would be considered to be the same variable.

Often, we want to check for many possibilities, and specify our application to

perform a particular action in each case. To achieve this, we use the Select Case

(VB) or switch (C#) construct:

Visual Basic

Select Case userName

Case "Zak"

Response.Redirect("ZaksPage.aspx")

Case "Mark"

Response.Redirect("MarksPage.aspx")

Case "Fred"

Response.Redirect("FredsPage.aspx")

Case Else

Response.Redirect("ErrorPage.aspx")

End Select

C#

switch (userName)

{

case "Zak":

Response.Redirect("ZaksPage.aspx");

break;

case "Mark":

Response.Redirect("MarksPage.aspx");

break;

case "Fred":

Response.Redirect("FredsPage.aspx");

break;

default:

Response.Redirect("ErrorPage.aspx");

break;

}

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Conditional Logic