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COBOL TUTORIAL
FOR BCA STUDENTS OF M G UNIVERSITY |
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The
PERFORM statement can be used to execute a group of
consecutive statements written elsewhere in the program.
We shall refer to this group of statements as the
range of the PERFORM statement. During execution,
when a PERFORM statement is encountered, a temporary
departure from the normal sequential execution takes
place and the statements contained in the specified
range are executed. Upon execution of the said statements,
the control implicitly returns to the next statement
following the PERFORM statement. It is also possible
to get the statements in the said range executed repetitively
for a specified number of times or until a condition
is satisfied.
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The statement group beginning with the first statement
of the procedure named in procedure-name-1 and ending
with the last statement of the procedure names in
procedurename- 2, constitutes the range consists of
the statements contained in the procedure referred
to by procedure-name-1. when the simple PERFORM statement
is executed, this range is executed only once.
Example:
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In this example, CALCULATE-TAX is
either a section name or paragraph name. Suppose it
is a section name. All the statements contained in
this section will be executed as a result of the execution
of the PERFORM statement and after the execution of
these statements, the control will come back to the
statement following the PERFORM statement.
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Suppose,
BEGIN-CALCULATION and END-CALCULTION are paragraph
names. The execution of the above PERFORM statement
will cause the execution of the group of the statements
starting with the first statement of BEGIN-CALCULATION
and ending with the last statement of end-calculation.
It may be noted that there may be other paragraphs
in between these two paragraphs. All these paragraphs
area also included in the range. Upon the execution
of the range, the control returns to the statement
following the PERFORM statement.
It may be noted that the return of control after the
execution of the statements in the specified range
takes place implicitly. This means that at the end
of the range, the programmer should not put any statement
(such as GO TO) to transfer the control explicitly
to the statement following the PERFORM statement.
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Important:
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A
GO TO statement is allowed within the range
of a PERFORM statement. However, it is the responsibility
of the programmer to ensure that the control
Ultimately reaches the last statement of the
range. |
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There
is no restriction as to what can be the last
statement of a range except that it cannot be
a GO TO statement. When an IF sentence is used
at the end of a range, the next sentence (specified
implicitly or explicitly) for that IF sentence
refers to the return mechanism. |
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The
use of a PERFORM statement within the range
of another PERFORM Statement is allowed. The
sequence of ranges specified in the Nested PERFORM
statements should neither overlap nor share
the same Terminal statement. |
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