Professional

Following the switch statement rules
The switch statement is very useful, but unfortunately, you can’t always use it when you might like to.
Any switch statement you write must adhere to the following rules:
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You can use switch only on certain data types, such as int, char, or string. With any other types
(including float and double), you must use an if statement.
The case labels must be constant expressions, such as 42 if the switch data type is an int, '4' if
the switch data type is a char, or "42" if the switch data type is a string. If you need to calculate
your case label values at run time, you must use an if statement.
The case labels must be unique expressions. In other words, two case labels cannot have the
same value.
You can specify that you want to run the same statements for more than one value by
providing a list of case labels and no intervening statements, in which case the code for the
final label in the list is executed for all cases in that list. However, if a label has one or more
associated statements, execution cannot fall through to subsequent labels; in this case, the
compiler generates an error. The following code fragment illustrates these points:
switch (trumps)
{
case Hearts :
case Diamonds :
color = "Red";
break;
case Clubs :
color = "Black";
case Spades :
color = "Black";
break;
}
// Fall-through allowed - no code between labels
// Code executed for Hearts and Diamonds
// Error - code between labels
Note The break statement is the most common way to stop fall-through, but you can also
use a return statement to exit from the method containing the switch statement or a throw
statement to generate an exception and abort the switch statement. The throw statement
is described in Chapter 6, “Managing errors and exceptions.”
switch fall-through rules
Because you cannot accidentally fall through from one case label to the next if there is any
intervening code, you can freely rearrange the sections of a switch statement without affecting
its meaning (including the default label, which by convention is usually—but does not have to
be—placed as the last label).
C and C++ programmers should note that the break statement is mandatory for every case
CHAPTER 4 Using decision statements 101