TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL STATEMENTS
where:
case selector
specifies an expression that evaluates to any
scal~r type except a real type.
case-label list specifies one or more constants of the same
type as the case selector, separated by
commas.
Each case-label list is associated with a statement that may be
executed. The list contains the value of the case-selector expression
for which the system executes the associated statement. You can
specify the case labels in any order. However, the difference between
the largest and smallest labels must not exceed 1000. Each case label
can appear only once within a CASE statement, but can appear in other
CASE statements.
At run time, the system evaluates the case-selector expression and
chooses which statement to execute. If the value of the case-selector
expression does not appear in any case-label list, the system executes
the statement in the OTHERWISE clause.
If the value of the case-selector expression does not match one of the
case labels and you omit the OTHERWISE clause, the status of the CHECK
run-time option determines the action that the system takes. Refer to
Section 8.4.3 for run-time options. If CHECK is enabled, the system
prints an error message and terminates execution. If CHECK is not
enabled, execution continues with the statement following the CASE
statement.
Example 1
CASE Ase OF
END~
5,6 IF Birth_Month> Se? THEN Grade l= 1 ELSE Grade != 0;
7 BEGIN
Grade := 2;
ReadinS_Skill := TRUE
END;
8 Grade:= 3
At run time, the system evaluates Age and executes one of the
statements. If Age is not equal to 5, 6, 7, or 8, and the CHECK
option is enabled, an error occurs and execution is terminated.
Example 2
CASE Ase OF
5,6 IF Birth_Month> Be? THEN Grade != 1 ELSE Grade := 0;
7 BEGIN
Grade != 2;
ReadinS_Skill := TRUE
END;
8 ! Grade := 3
OTHERWISE Grade := 0
An OTHERWISE clause is added in this example. If the value of Age is
not 5, 6, 7, or 8, the value a is assigned to the variable Grade.
5-7