Cob Basics 5
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Transcript of Cob Basics 5
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IF Statement
Format for IF statements
IF condition-1[THEN]
imperative statement-1 . . .
[ELSE
imperative statement-2 . . . ]
[END-IF]
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IF Statement
Using Relational Operators in Place of Words.
RELATIONAL OPERATORS
Symbol Meaning< IS LESS THAN
> IS GREATER THAN
= IS EQUAL TO
COBOL 85 only
= IS GREATER THAN OR EQUAL TO
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IF Statement
There are times when you might want to execute a series of steps
only if a certain condition does not exist.
The COBOL expression CONTINUE (COBOL 85) or NEXTSENTENCE (COBOL 74) will enable you:
(1) to avoid performing any operation if a condition exists
(2) to execute instructions only if the ELSE condition is met
Do Not Mix Field Types in a Comparison.
Conditional statements must use fields with the same data types to
obtain proper results.
Numeric Fields Should Not Contain Blanks
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IF Statement
A nested conditional is a conditional in which an IF statementitself can contain additional IF clauses.
IF condition-1
statement-1ELSE
IF condition-2
statement-2
ELSE
statement-3END-IF
END-IF
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IF Statement
To perform an operation or a series of operations if any one of
several conditions exists, use a compound OR condition.
This means that if any one of several conditions exists, the
imperative statement(s) specified will be executed.
By using OR in a compound conditional, any of the conditions
specified causes execution of the statement(s).
If none of the conditions is met, the computer executes either the
ELSE clause, if coded, or the next sentence.
Any number of conditions separated by ORs may be coded in a
single statement.
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IF Statement
We can test whether a field is POSITIVE, NEGATIVE, or ZEROwith a sign test.
We can test for the type of data in a field by coding IF identifier- 1
IS NUMERIC or IF identifier-1 IS ALPHABETIC
Format
IF identifier-1 IS [NOT ]
{{GREATER THAN (>)}
{LESS THAN (
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IF Statement
IF identifier-1 IS [NOT]
{{ NUMERIC}
{POSITIVE}
{NEGATIVE }
{ZERO}
{ALPHABETIC}
{ALPHABETIC-UPPER*}{ALPHABETIC-LOWER*}}
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Evaluate Statement
EVALUATE {identifier-1}
{expression-1}WHEN condition-1 imperative- statement-1 . . .
[WHEN OTHER imperative-statement-2]
[END-EVALUATE]
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Perform Statement
In-Line PERFORMPERFORM
Statements to
be executed
END-PERFORM
An in-line PERFORM begins with the word PERFORM, is followed
by statements to be executed, and ends with an END-PERFORM
scope terminator.
All instructions within the PERFORM ... END-PERFORM are
executed in sequence.
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Perform Statement
PERFORM Paragraph-Name
PERFORM [paragraph-name-1]
The PERFORM paragraph-name statement will:
1. Execute all instructions in the named paragraph.
2. Transfer control to the next instruction in sequence, after the
PERFORM paragraph-name.
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Perform Statement
Expanded format for the PERFORM paragraph-name statement:
PERFORM paragraph-name-1 {THROUGH} {THRU}
paragraph-name-2
The PERFORM paragraph-name executes all statementsbeginning at paragraph-name-1 until the end of paragraph-name-2
is reached.
Control is then transferred to the statement directly following thePERFORM.
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EXIT Statement
EXIT is a COBOL reserved word that performs no operation.
It is used to allow execution to pass over other statements or to
transfer control back to the statement following the originalPERFORM.
It is used, when necessary, as an end point in a paragraph being
performed.
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Perform Statement
The format of a PERFORM UNTIL ... is:
Format 2
PERFORM [paragraph-name-1] [{THROUGH} {THRU}
paragraph-name-2]
UNTIL condition-1
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Perform Statement
FormatPERFORM paragraph-name-1 [{THROUGH} {THRU}
paragraph-name-2]
VARYING identifier-1 FROM {identifier-2}{integer-1}
BY {identifier-3} {integer-2}
UNTIL condition-1
1. The innermost PERFORM VARYING loop is executed first.
2. The next outer PERFORM VARYING loop in sequence is then
executed.
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Perform Statement
PERFORM paragraph-name-1
[WITH TEST {BEFORE} {AFTER}]
UNTIL condition-1
The WITH TEST AFTER clause can also be used with the
VARYING option of the PERFORM. The format is: PERFORM
WITH TEST AFTER VARYING ....