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 its 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