HP OpenVMS Systems Documentation

HP COBOL
Reference Manual

Like statements, COBOL sentences also can be compiler-directing, imperative, or conditional. Sentence type depends upon the types of statements the sentence contains. Table 6-2 summarizes the contents of the three types of COBOL sentences. The remaining text in this section describes each type of statement and sentence in greater detail.

A compiler-directing statement causes the compiler to take an action during compilation. The verbs COPY, REPLACE, RECORD, and USE define compiler-directing statements. A compiler-directing sentence can contain other statements but it must contain only one compiler-directing statement. The compiler-directing statement must be the last statement in the sentence and must be followed immediately by a period.

6.1.2 Imperative Statements and Sentences

An imperative statement specifies an unconditional action for the program. It must contain a verb and the verb's operands, and cannot contain any conditional phrases. For example, the following statements are imperative:

OPEN INPUT FILE-A

COMPUTE C = A + B

However, the following statement is not imperative because it contains the phrase, ON SIZE ERROR, which makes the program's action conditional:

COMPUTE C = A + B ON SIZE ERROR PERFORM NUM-TOO-BIG.

In the Procedure Division rules, an imperative statement can be a sequence of consecutive imperative statements. The sequence must end with: (1) a separator period or (2) any phrase associated with a statement that contains the imperative statement. For example, the following sentence contains a sequence of two imperative statements following the AT END phrase.

READ FILE-A AT END PERFORM NO-MORE-RECS
                   DISPLAY "No more records."     END-READ.

An imperative sentence contains only imperative statements and ends with a separator period.

6.1.3 Conditional Statements and Sentences

A conditional statement determines a condition's truth value. (A truth value is either a yes or no answer to the question, "Is the condition true?".) The statement uses the truth value generated by the program to determine subsequent program action.

Conditional statements are as follows:

• An EVALUATE, IF, RETURN, or SEARCH statement
• An ACCEPT statement with the [NOT] AT END or [NOT] ON EXCEPTION phrase
• A DISPLAY statement with the [NOT] ON EXCEPTION phrase
• A READ statement with the [NOT] AT END or [NOT] INVALID KEY phrase
• A WRITE statement with the [NOT] INVALID KEY or [NOT] END-OF-PAGE phrase
• A DELETE, REWRITE, or START statement with the [NOT] INVALID KEY phrase
• An arithmetic statement (ADD, COMPUTE, DIVIDE, MULTIPLY, SUBTRACT) with the [NOT] ON SIZE ERROR phrase
• A STRING or UNSTRING statement with the [NOT] ON OVERFLOW phrase
• A CALL statement with the [NOT] ON EXCEPTION or [NOT] ON OVERFLOW phrase

A conditional sentence is a conditional statement that ends with a separator period. It can include an optional preceding imperative statement. For example, the following sentence is conditional even though it contains the imperative statement, GO TO PROC-A:

READ FILEA AT END GO TO PROC-A.

The program interprets this sentence to mean "If not at the end of the file, read the next record; otherwise, go to PROC-A."

6.1.4 Scope of Statements

Scope terminators delimit the scope of some Procedure Division statements.

The scope of statements contained (nested) in other statements can also terminate implicitly. When statements are contained in other statements, a separator period (that terminates the sentence) terminates all nested statements as well.

In the following example, the separator period terminates the IF, MOVE, and PERFORM statements:

IF ITEMA = ITEMB
   MOVE ITEMC TO ITEMB
   PERFORM PROCA.

In the following example, the ELSE phrase of the IF statement terminates the scope of the READ and the first MOVE statements:

IF ITEMA = ITEMB
   READ FILEA
        AT END MOVE ITEMC TO ITEMB
ELSE
   MOVE ITEMD TO ITEME.

A delimited-scope statement is a special category of statement used in structured programming. A delimited-scope statement is any statement that includes its explicit scope terminator. See Section 6.3.4 for a list of explicit scope terminators.

A delimited-scope statement can be nested in another delimited-scope statement with the same verb. Then, each explicit scope terminator terminates the statement that begins with the closest unpaired preceding occurrence of the verb.

In the following example, the END-IF after the ADD statements (line 8) terminates the IF on line 5. The END-IF after the SUBTRACT (line 10) terminates the IF on line 3. The scope of the first IF statement (line 1) is terminated by the separator period on line 11.

1. IF ITEMA = ITEMB
2. MULTIPLY ITEMH BY ITEMI
3. IF ITEMI > 18
4. MOVE ITEMC TO ITEMD
5. IF ITEMD > ITEME
6. ADD ITEME TO ITEMF
7. ADD ITEMG TO ITEMH
8. END-IF
9. SUBTRACT 6 FROM ITEMH
10. END-IF
11. PERFORM PROCA.

Every user-defined name in a COBOL program names a resource. (See the section on User-Defined Words in Section 1.2.1.) To use a resource, however, a statement in a COBOL program must contain a reference that uniquely identifies that resource. Qualification, reference modification, and subscripting or indexing allow unique and unambiguous references to that resource. Qualified procedure-names allow uniqueness of reference to procedures, and qualified condition-names allow uniqueness of reference to condition-names.

When you assign the same name in separate (contained) programs to two or more occurrences of a resource, certain conventions apply that limit the scope of names. Name scoping and scope of names are COBOL language terms that describe the methods for resolving references to user-defined words in a contained program environment. (See Section 6.2.6, Scope of Names.)

Some user-defined words can be made available to every program in the run unit. (See the Section 5.3.21 clause in Chapter 5.) These words are called external data. Other user-defined words can be made available to programs contained within the program that defines that resource. (See the Section 5.3.25 clause in Chapter 5.) These words are called global data.

6.2.1 Qualification

A reference to a user-defined word is unique if one or more of the following conditions exists:

• No other name has the same spelling, including hyphenation.
• It is part of a REDEFINES clause. (The reference following the word REDEFINES is unique because of the placement of the REDEFINES clause.) See the Syntax Rules for the Section 5.3.40 clause.
• Scoping rules make it unique. (See Section 6.2.6, Scope of Names.)

A nonunique name within a hierarchy of names can be used in more than one place in your program. Unless you are redefining it, you must refer to this nonunique name using one or more higher-level names in the hierarchy. These higher-level names are called qualifiers. Using them to achieve uniqueness of reference is called qualification.

To make your reference unique, you need not specify all available qualifiers for a name, only those necessary to eliminate ambiguity.

Consider the following two record descriptions:

01 REC1.
    05 ITEMA       PIC XX.
    05 ITEMB       PIC X(20).

01 REC2.
    05  GROUP1.
        10  ITEMA  PIC 9(5).
        10  ITEMB  PIC X(3).
    05  GROUP2.
        10  ITEMC  PIC X(4).
        10  ITEMD  PIC X(8).

ITEMA and ITEMB appear in both record descriptions. Therefore, you must use qualifiers when you refer to these items in Procedure Division statements. For example, all of the following references to ITEMA are unique: ITEMA OF GROUP1, ITEMA OF REC1, ITEMA IN GROUP1 OF REC2.

Regardless of the preceding, you cannot use the same data-name as:

• The name of an external record and as the name of any other external data item in any program contained within or containing the program describing the external data record
• The name of an item possessing the global attribute and as the name of any other data item in the program describing the global data item