switch, case, otherwise

Execute one of several groups of statements

Syntax

switch switch_expression
   case case_expression
      statements
   case case_expression
      statements
    ...
   otherwise
      statements
end

Description

switch switch_expression, case case_expression, 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, case_expression == switch_expression.

• For character vectors, strcmp(case_expression,switch_expression) == 1.

• For objects that support the eq function, case_expression == switch_expression. The output of the overloaded eq function must be either a logical value or convertible to a logical value.

• For a cell array case_expression, at least one of the elements of the cell array matches switch_expression, 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 switch_expression must be a scalar or character vector. An evaluated case_expression 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.

Examples

Compare Single Values

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.

positive one

Repeat the code and enter the number 3.

other value

Compare Against Multiple Values

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 case_expression cannot include relational operators such as < or > for comparison against the switch_expression. 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

  result is 52

• 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 MATLAB break statement ends execution of a for or while loop, but does not end execution of a switch statement. This behavior is different than the behavior of break and switch in C.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

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.

HDL Code Generation

Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

• The conditional expression in a switch or case 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.