SELECT CASE Construct

This is a useful control construct if one of several paths through an algorithm must be chosen based on the value of a particular expression. SELECT CASE is more efficient than ELSEIF because there is only one expression that controls the branching. The expression needs to be evaluated once and then control transferred to whichever branch corresponds to the expressions value. An IF .. ELSEIF ... has the potential to have a different expression to evaluate at each branch point making it less efficient.

The syntax is as follows,

 
 [    name   : ] SELECT CASE    case-expr   

		 [ CASE    case-selector    [    name    ]

		 		    exec-stmts    ] ...

		 [ CASE DEFAULT [    name    ]

		 		    exec-stmts    ]

END SELECT  [    name    ]

Note,

• the  case-expr must be scalar and INTEGER, LOGICAL or CHARACTER valued;
• there may be any number of general CASE statements but only one CASE DEFAULT branch;
• the  case-selector must be a parenthesised single value or a range (section with a stride of one), for example, (.TRUE.) or (99:101). A range specifier is a lower and upper limit separated by a single colon. One or other of the bounds is optional giving an open ended range specifier.
• the  case-expr is evaluated and compared with the  case-selector s in turn to see which branch to take.
• if no branches are chosen then the CASE DEFAULT is executed (if present).
• when the  exec-stmts in the selected branch have been executed, control jumps out of the CASE construct (via the END SELECT statement).
• as with other similar structures it is not possible to jump into a CASE construct.

CASE constructs may be named -- if the header is named then so must be the END SELECT statement. If any of the CASE branches are named then so must be the SELECT statement and the END statement

• Example Of SELECT CASE Construct