The switch Statement (GNU Octave (version 6.0.92))

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### 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 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

Next: The while Statement, Previous: The if Statement, Up: Statements [Contents][Index]