switch - Execute one of several groups of statements - MATLAB (original) (raw)

switch, case, otherwise

Execute one of several groups of statements

Syntax

switch switchexpression case caseexpression statements case caseexpression statements ... otherwise statements end

Description

switch _`switchexpression`_, case _`caseexpression`_, end evaluates an expression and chooses to execute one of several groups of statements. Each choice is a case.

The switch block tests each case until one of the case expressions is true. A case is true when:

• For numbers, _`caseexpression`_ == _`switchexpression`_.
• For character vectors and strings,strcmp(_`caseexpression`_,_`switchexpression`_) == 1. Cell arrays of character vectors are a special case where case will match if at least one element of the cell array matches.
• For objects that support the eq function,_`caseexpression`_ ==_`switchexpression`_. The output of the overloaded eq function must be either a logical value or convertible to a logical value.
• For a cell array caseexpression, at least one of the elements of the cell array matches switchexpression, as defined above for numbers, character vectors, and objects.

When a case expression is true, MATLAB® executes the corresponding statements and exits the switch block.

An evaluated switchexpression must be a scalar or character vector. An evaluated caseexpression must be a scalar, a character vector, or a cell array of scalars or character vectors.

The otherwise block is optional. MATLAB executes the statements only when no case is true.

example

Examples

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Display different text conditionally, depending on a value entered at the command prompt.

n = input('Enter a number: ');

switch n case -1 disp('negative one') case 0 disp('zero') case 1 disp('positive one') otherwise disp('other value') end

At the command prompt, enter the number 1.

Repeat the code and enter the number 3.

Determine which type of plot to create based on the value of plottype. If plottype is either 'pie' or 'pie3', create a 3-D pie chart. Use a cell array to contain both values.

x = [12 64 24]; plottype = 'pie3';

switch plottype case 'bar' bar(x) title('Bar Graph') case {'pie','pie3'} pie3(x) title('Pie Chart') otherwise warning('Unexpected plot type. No plot created.') end

Tips

• A caseexpression cannot include relational operators such as < or > for comparison against the switchexpression. To test for inequality, use if, elseif, else statements.
• The MATLAB switch statement does not fall through like a C language switch statement. If the first case statement is true, MATLAB does not execute the other case statements. For example:
  result = 52;
  switch(result)
  case 52
  disp('result is 52')
  case {52, 78}
  disp('result is 52 or 78')

end

• Define all variables necessary for code in a particular case within that case. Since MATLAB executes only one case of any switch statement, variables defined within one case are not available for other cases. For example, if your current workspace does not contain a variable x, only cases that define x can use it:
  switch choice
  case 1
  x = -pi:0.01:pi;
  case 2
  % does not know anything about x

end

• The MATLABbreak statement ends execution of afor or while loop, but does not end execution of a switch statement. This behavior is different than the behavior of break andswitch in C.

Extended Capabilities

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Usage notes and limitations:

• If all case expressions are scalar integer values, then the code generator produces a C switch statement. At run time, if the switch value is not an integer, then the code generator produces an error.

• When the case expressions contain noninteger or nonscalar values, the code generator produces C if statements in place of a C switch statement.

• The conditional expression in a switch orcase statement must use only:

  • uint8, uint16,uint32, int8,int16, or int32 data types
  • Scalar data

• If multiple case statements make assignments to the same variable, the numeric type and fimath specification for that variable must be the same in every case statement.

Version History

Introduced before R2006a