Info Catalog octave: The if Statement octave: Statements octave: The while Statement

octave: The switch Statement

 
 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
 

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Info Catalog octave: The if Statement octave: Statements octave: The while Statement