See Also

The Case Statement lists the alternatives that may be activated depending on the value of the variable, group, or expression following the CASE keyword.

The following example shows a Case Statement:

CASE f[].q IS
   WHEN H"00" =>
      addr[] = 0;
      s = a & b;
   WHEN H"01" =>
      count[].d = count[].q + 1;
   WHEN H"02", H"03", H"04" =>
      f[3..0].d = addr[4..1];
   WHEN OTHERS =>
      f[].d = f[].q;
END CASE;

The Case Statement has the following characteristics:

• The keywords CASE and IS enclose a Boolean expression, group, or state machine (in the example shown above, f[].q).

• The Case Statement is terminated by the keywords END CASE and a semicolon (;).

• One or more unique alternatives are listed in the WHEN clauses in the body of the Case Statement. Each WHEN clause begins with the keyword WHEN.

• In each alternative WHEN clause, one or more comma-separated constant values are followed by an arrow symbol (=>). In this example, the H"02", H"03", and H"04" constant values are listed in a single WHEN clause; the H"00" and H"01" constant values are listed in separate WHEN clauses.

• If the Boolean expression following the CASE keyword evaluates to a specific alternative, all the behavioral statements following the arrow are activated. In the example shown above, if f[].q evaluates to H"01", the Boolean equation count[].d = count[].q + 1 is activated.

• When no other alternative is true, the optional keywords WHEN OTHERS define the default alternative. In the example shown above, if f[].q does not equal H"00", H"01", or H"CF", the Boolean equation f[].d = f[].q is activated.

• The Defaults Statement defines the default behavior if the WHEN OTHERS clause is not used.

• If the Case Statement is used to define the transitions of a state machine, the keywords WHEN OTHERS cannot be used to recover from illegal states of an n-bit state machine unless the state machine contains exactly 2^n states.

• Each behavioral statement ends with a semicolon (;).

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