The switch Statement - Untitled
Description: Untitled

Next: The while Statement, Previous: The if Statement, Up: Statements

### 10.2 The `switch` Statement

It is very common to take different actions depending on the value of one variable. This is possible using the `if` statement in the following way

         if (X == 1)
           do_something ();
         elseif (X == 2)
           do_something_else ();
         else
           do_something_completely_different ();
         endif

This kind of code can however be very cumbersome to both write and maintain. To overcome this problem Octave supports the `switch` statement. Using this statement, the above example becomes

         switch (X)
           case 1
             do_something ();
           case 2
             do_something_else ();
           otherwise
             do_something_completely_different ();
         endswitch

This code makes the repetitive structure of the problem more explicit, making the code easier to read, and hence maintain. Also, if the variable `X` should change it's name, only one line would need changing compared to one line per case when `if` statements are used.

The general form of the `switch` statement is

         switch expression
           case label
             command_list
           case label
             command_list
           ...

           otherwise
             command_list
         endswitch

where label can be any expression. However, duplicate label values are not detected, and only the command_list corresponding to the first match will be executed. For the `switch` statement to be meaningful at least one `case` label command_list clause must be present, while the `otherwise` command_list clause is optional.

If label is a cell array the corresponding command_list is executed if any of the elements of the cell array match expression. As an example, the following program will print ``Variable is either 6 or 7`'.

         A = 7;
         switch A
           case { 6, 7 }
             printf ("variable is either 6 or 7\n");
           otherwise
             printf ("variable is neither 6 nor 7\n");
         endswitch

As with all other specific `end` keywords, `endswitch` may be replaced by `end`, but you can get better diagnostics if you use the specific forms.

One advantage of using the `switch` statement compared to using `if` statements is that the labels can be strings. If an `if` statement is used it is not possible to write

         if (X == "a string") # This is NOT valid

since a character-to-character comparison between `X` and the string will be made instead of evaluating if the strings are equal. This special-case is handled by the `switch` statement, and it is possible to write programs that look like this

         switch (X)
           case "a string"
             do_something
           ...
         endswitch