CHAPTER 9 STATEMENTS

The switch Statement

The switch statement implements multiway branching. Figure 9-3 shows the syntax and structure of the switch statement.

•The switch statement contains zero or more switch sections.

•Each switch section starts with one or more switch labels.

Figure 9-3. Structure of a switch statement

Switch labels have the following form:

case ConstantExpression:

The flow of control through the structure in Figure 9-3 is the following:

•The test expression, TestExpr, is evaluated at the top of the construct.

•Each switch section must end with the break statement or one of the other four jump statements.

—The jump statements are break, return, continue, goto, and throw, and they are described later in this chapter.

—Of the five jump statements, the break statement is the most commonly used for ending a switch section. The break statement branches execution to the end of the switch statement. We’ll cover all the jump statements later in this chapter.

•If the value of TestExpr is equal to the value ConstExpr1, the constant expression in the first switch label and then the statements in the statement list following the switch label are executed, until the one of the jump statements is encountered.

•The default section is optional, but if it is included, it must end with one of the jump statements.

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CHAPTER 9 STATEMENTS

Figure 9-4 illustrates the general flow of control through a switch statement. You can modify the flow through a switch statement with a goto statement or a return statement.

Figure 9-4. The flow of control through a switch statement

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CHAPTER 9 STATEMENTS

A Switch Example

The following code executes the switch statement five times, with the value of x ranging from 1 to 5. From the output, you can tell which case section was executed on each cycle through the loop.

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More on the switch Statement

A switch statement can have any number of switch sections, including none. The default section is not required, as shown in the following example. It is, however, generally considered good practice to include it, since it can catch potential errors.

For example, the switch statement in the following code has no default section. The switch statement is inside a for loop, which executes the statement five times, with the value of x starting at 1 and ending at 5.

for( int x=1; x<6; x++ )

{

switch( x )

{

case 5:

Console.WriteLine("x is {0} -- In Case 5", x); break;

}

}

This code produces the following output:

x is 5 -- In Case 5

The following code has only the default section:

for( int x=1; x<4; x++ )

{

switch( x )

{

default:

Console.WriteLine("x is {0} -- In Default case", x); break;

}

}

This code produces the following output:

x is 1 -- In Default case x is 2 -- In Default case x is 3 -- In Default case

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