Copyright (c) 1994 J. Adams, W. Brainerd, J. Martin, and B. Smith.
All rights reserved.
This file may not be copied without permission of the authors.

11 CASE Construct

The CASE construct may be used to select for execution at most one of the blocks in the construct. Selection is based on a scalar value of type integer, character, or logical. A CASE construct may be named. It permits the following control flow:

Examples:

! Character example               ! Integer example
SELECT CASE (STYLE)                                     RANGES: &
  CASE DEFAULT                    SELECT CASE (ITEM)
    CALL SOLID (X1,Y1,X2,Y2)        CASE (1:7, 52:81)   RANGES
  CASE ("DOTS")                       BIN1 = BIN1 + 1.0
    CALL DOTS (X1,Y1,X2,Y2)         CASE (8:32, 51, 82) RANGES
  CASE ("DASHES")                     BIN2 = BIN2 + 1.0
    CALL DASHES (X1,Y1,X2,Y2)       CASE (33:50, 83: )  RANGES
END SELECT                            BIN3 = BIN3 + 1.0
                                    CASE DEFAULT        RANGES
! Logical Example                     WRITE (*, "(`BAD ITEM')")
LIMIT: SELECT CASE (X > X_MAX)    END SELECT            RANGES
   CASE (.TRUE.)
      Y = X * 0.9
   CASE (.FALSE.)
      Y = 1.0 / X
END SELECT LIMIT

Tip: For program clarity, use an IF-THEN-ELSE construct rather than a logical CASE construct.

Related Topics:

Expressions: Initialization
IF Construct and Statement

To Read More About It:

ISO 1539 : 1991, Fortran Standard, 8.1.3
Fortran 90 Handbook, 8.4
Programmer's Guide to Fortran 90, 2.4

A CASE construct is:

[ case-construct-name : ] SELECT CASE ( case-expression )
[ CASE ( case-value-range-list ) [ case-construct-name ]
block ]...
[ CASE DEFAULT [ case-construct-name ]
block ]
END SELECT [ case-construct-name ]

A case-value-range is one of:

case-value [ : case-value ]
case-value :
: case-value

Things To Know:

1. The case expression and all case values must be scalar and of the same type. The types allowed are integer, character, and logical. If the character type is used, different lengths are allowed. If the logical type is used, a case value range (with a :) is not permitted. The case values must be initialization expressions. Overlapping case values and case ranges are prohibited.
2. The case value range list enclosed in parentheses and the keyword DEFAULT are called selectors. The case expression must select at most one of the selectors. If the case expression matches one of the values or falls in one of the ranges, the block following the matched selector is the one executed. If there is no match, the block following the DEFAULT selector is executed; it need not be last. If there is no match and no DEFAULT selector, no code block is executed. A block may be empty.
3. Control constructs may be nested, in which case a program may be easier to read if the constructs are named. If a construct name appears on a SELECT CASE statement, the same name must appear on the corresponding END SELECT statement and is optional on CASE statements of the construct.
4. A construct name must not be used as the name of any other entity such as a variable, named constant, procedure, type, namelist group, or another construct.
5. Branching to any statement in a CASE construct, other than the initial SELECT CASE statement, from outside the construct is not permitted. Branching to an END SELECT statement from within the construct is permitted.