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EVALUATE Statement The EVALUATE statement adds a multi-condition case construct to COBOL. This statement causes a set of subjects to be evaluated and compared with a set of objects. The results of these evaluations determine the subsequent sequence of code execution. SyntaxSubjects and Objects The operands or the words TRUE and FALSE that appear before the first WHEN phrase of the EVALUATE statement are referred to individually as subjects. Collectively, they are referred to as the set of subjects. The operands or the words TRUE, FALSE, and ANY that appear in a WHEN phrase of an EVALUATE statement are individually called objects. Collectively, they are called the set of objects. The words THROUGH and THRU are equivalent. Two operands connected by a THROUGH phrase must be of the same class. The two connected operands constitute a single object. The number of objects within each set of objects must be equal to the number of subjects. Correspondence Between Subjects and Objects. A subject-object pair consists of a subject and object having the same ordinal position within each set. Each pair must conform to the following rules: * Identifiers, literals, and arithmetic expressions must be valid operands for a comparison between the subject and object. * Conditions or the words TRUE or FALSE appearing as an object must correspond to a conditional expression or the words TRUE or FALSE. * The word ANY may correspond to a selection subject of any type. Evaluation of Subjects and Objects. Execution of the EVALUATE statement operates as if each subject and object were evaluated and assigned a numeric or nonnumeric value, a range of numeric or nonnumeric values, or a truth value (TRUE or FALSE). These values are determined as follows: * Any subject or object specified by an identifier, without either the NOT or the THROUGH phrases, is assigned the value and class of the data item referenced by the identifier. * Any subject or object specified by a literal, without either the NOT or the THROUGH phrases, is assigned the value and class of the specified literal. When an object is assigned the figurative constant ZERO, it is assigned the class of the corresponding subject. * Any subject or object in which an expression is specified as an arithmetic expression without either the NOT or the THROUGH phrases, is assigned a numeric value according to the rules for evaluating an arithmetic expression. (Refer to Chapter 8 , under "Arithmetic Expressions".) * A subject or object specified by a conditional expression is assigned a truth value (TRUE or FALSE) according to the rules for evaluating conditional expressions. (Refer to Chapter 8 , "Conditional Expressions.") * A subject or object specified by the words TRUE or FALSE is assigned the appropriate truth value. * No further evaluation is done for an object specified by the word ANY. * If the THROUGH phrase is specified for an object, without the NOT phrase, the range of values includes all values of the subject that are greater than or equal to the first operand and less than or equal to the second operand. * If the NOT phrase is specified for an object, the values assigned to that item are all values that are not equal to the value, or included in the range of values, that would have been assigned to the item without the NOT phrase. Refer to Chapter 8 , "Relation Conditions," for more information on NOT phrases. Comparison Operation of EVALUATE The execution of the EVALUATE statement proceeds as if the values assigned to the subjects and objects were compared, to determine if any WHEN phrase satisfies the set of subjects. This comparison proceeds as follows: 1. A subject-object pair comparison is satisfied if the following conditions are true: a. If the items being compared are assigned numeric, nonnumeric, or a range of numeric or nonnumeric values, the comparison is satisfied if the value, or one of the range of values, assigned to the object is equal to the value assigned to the subject. b. If the items being compared are assigned truth values, the comparison is satisfied if the items are assigned the identical truth values. c. If the object being compared is specified by the word ANY, the comparison is always satisfied, regardless of the value of the subject. 2. If the above comparison is satisfied for every object within the set of objects being compared, the first WHEN phrase for which each subject-object pair comparison is satisfied is selected as the one that satisfies the set of subjects. 3. If the above comparison is not satisfied for one or more objects within the set of objects being compared, that set of objects does not satisfy the set of subjects. 4. This procedure is repeated for subsequent sets of objects in the order of their appearance in the source program. The comparison operation continues until either a WHEN phrase that satisfies the set of subjects is selected or until all sets of objects are exhausted. Execution of EVALUATE After the comparison operation is completed, execution of the EVALUATE statement proceeds as follows: 1. If a WHEN phrase is selected, execution continues with the first imperative statement following the selected WHEN phrase. [REV BEG] If a WHEN phrase is followed by other WHEN phrases with no intervening imperative statement, the WHEN conditions are ORed together. In other words, if any of the WHEN phrases is selected, the first imperative statement that follows is executed, even if that imperative statement is part of a following WHEN phrase. See the following section for an example. Use the CONTINUE statement to indicate no operation on a WHEN clause. See the following section for examples.[REV END] 2. If no WHEN phrase is selected and a WHEN OTHER phrase is specified, execution continues with the imperative statement following the WHEN OTHER phrase. 3. The execution of the EVALUATE statement is terminated when execution reaches the end of the imperative statement of the selected WHEN phrase, or when no WHEN phrase is selected and no WHEN OTHER phrase is specified. Examples [REV BEG] The following example shows an EVALUATE statement with two data items (HOURS-WORKED and EXEMPT) as subjects:[REV END] EVALUATE HOURS-WORKED ALSO EXEMPT WHEN 0 ALSO ANY PERFORM NO-PAY WHEN NOT 0 ALSO "Y" PERFORM SALARIED WHEN 1 THRU 40 ALSO "N" PERFORM HOURLY-PAY WHEN NOT 1 THRU 40 ALSO "N" PERFORM OVERTIME-PAY WHEN OTHER DISPLAY HOURS-WORKED DISPLAY EXEMPT MOVE 0 TO HOURS-WORKED END-EVALUATE. [REV BEG] The following shows a relation condition (GRADE > 3.0) and a data item (COLLEGE-CODE) as the subjects of an EVALUATE:[REV END] EVALUATE GRADE > 3.0 ALSO COLLEGE-CODE WHEN TRUE ALSO "01" PERFORM DEANS-LIST-AGGIES WHEN TRUE ALSO "02" PERFORM DEANS-LIST-S-AND-H WHEN TRUE ALSO "03" PERFORM DEANS-LIST-ENG WHEN TRUE ALSO ANY PERFORM MISC-LIST END-EVALUATE. [REV BEG] The following shows two equivalent EVALUATE statements that illustrate that subjects and objects must be of the same type. The first EVALUATE statement shows the truth value, TRUE, as the subject and several condition name conditions as objects. The second shows the data item INPUT-FLAG as the subject and nonnumeric literals as objects. Notice also that if INPUT-FLAG is "C", the EVALUATE statement executes the CONTINUE statement, which simply continues execution at the statement following the EVALUATE statement: WORKING-STORAGE SECTION. 01 INPUT-FLAG PIC X VALUE SPACE. 88 INPUT-YES VALUE "Y". 88 INPUT-NO VALUE "N". 88 INPUT-QUIT VALUE "Q". 88 INPUT-CONTINUE VALUE "C". : EVALUATE TRUE WHEN INPUT-CONTINUE CONTINUE WHEN INPUT-YES MOVE PROD-NO TO OUTPUT-REC WHEN INPUT-NO MOVE SPACES TO OUTPUT-REC WHEN INPUT-QUIT PERFORM TERMINATION-ROUTINE WHEN OTHER PERFORM GET-INPUT END-EVALUATE. [REV END] [REV BEG] EVALUATE INPUT-FLAG WHEN "Y" MOVE PROD-NO TO OUTPUT-REC WHEN "N" MOVE SPACES TO OUTPUT-REC WHEN "Q" PERFORM TERMINATION-ROUTINE WHEN "C" CONTINUE WHEN OTHER PERFORM GET-INPUT END-EVALUATE. The following example shows two WHEN phrases without an intervening imperative statement. If either the first or the second WHEN phrase is selected, that is, if NUMBER-OF-THINGS is either 1 or 2, the DISPLAY statement after WHEN 2 is executed: EVALUATE NUMBER-OF-THINGS WHEN 1 WHEN 2 DISPLAY "The value is 1 or 2" WHEN 3 STOP RUN WHEN OTHER DISPLAY "Input again." END-EVALUATE. [REV END]
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