====== CASE ======
===== case_statement =====
<code vhdl>
case expression is
     case_statement_alternative
     { case_statement_alternative }
end case [ case_label ] ;
</code>

===== Parents =====
  * function_statement_part
  * procedure_statement_part
  * process_statement_part

===== Further definition =====
==== label ====
  * [[.:bnf#identifier]]

==== expression ====
  * [[.:bnf#relation]] { and relation }
  * relation { or relation }
  * relation { xor relation }
  * relation [ nand relation ]
  * relation [ nor relation ]
  * relation { xnor relation }

==== case_statement_alternative ====
''**when** [[.:bnf#choices]] <nowiki> => </nowiki>'' \\
''     [[.:bnf#sequence_of_statements]]''

===== Examples =====
The value of bit //a// is checked. If it is //0// then //s// is assigned the value //0000// after 2 ns, otherwise it is assigned the value //1111// , also after 2 ns.
<code vhdl>
CASE a IS
   WHEN '0' => s <= "0000" AFTER 2 ns ;
   WHEN '1' => s <= "1111" AFTER 2 ns ;
END CASE ;
</code>

----

The value of the integer //int_value// is checked. If it is //0// then int is assigned the value //5// ; if it is //1// , //2// or //8// //int// is assigned the value of //int_value// ; if it is between //3// and //7// int is assigned the value //int_value + 5// ; if it is //9// no action is carried out. For all other values of //int_value// //int// is assigned the value //0// .
<code vhdl>
CASE int_value IS
   WHEN 0       => int := 5 ;
   WHEN 1 | 2 | 8 => int := int_value ;
   WHEN 3 TO 7  => int := int_value+5;
   WHEN 9       => NULL ;
   WHEN OTHERS    => int := 0 ;
END CASE ;
</code>

----

Depending on the value of the expression //two_bit '( a_enable & b_enable )//, //s// is assigned the corresponding value after a certain delay.
<code vhdl>
CASE two_bit'( a_enable & b_enable ) IS
   WHEN "00" => s <= zero AFTER 1 ns ;
   WHEN "10" => s <= a AFTER 1 ns ;
   WHEN "01" => s <= b AFTER 2 ns ;
   WHEN "11" => s <= one AFTER 1 ns ;
END CASE ;
</code>