TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL STATEMENTS
Example q
Ase~5
::::: Asps····[ 10+".7J'
Assume that the base type of the set variable Ages is the integer
subrange 0 .. 255. This exampJe assigns the value of the set expression
Ages- rlO+7] to the variable Ages.
5.3 CONDITIONAL STATEMENTS
A conditional statement selects a statement for execution depending on
the value of an expression. PASCAL provides three conditional
statements:
• IF-THEN statement
• IF-THEN-ELSE statement
• CASE statement
These are described in the following sections.
5.3.1 The IF-THEN Statement
The IF-THEN statement causes the conditional execution of a statement.
Fo rma t
IF expression THEN statement;
where:
expression
statement
specifies a Boolean expression.
indicates a simple or compound statement.
The statement is executed only if the value of the expression is TRUE.
If the value of the expression is FALSE, program control passes to the
statement following the IF-THEN statement.
The THEN clause can specify a compound statement. However, note that,
if you use the compound statement, you must not place a semicolon
between the words THEN and BEGIN. The example below shows a semicolon
immediately following the word THEN:
IF Da~
BEGIN
= Thurs THEN,
statement
(* misPlaced semicolon *)
END;
As a result of the misplaced semicolon, the empty statement becomes
the object of the THEN clause. In this example, the compound
statement following the IF-THEN statement is executed regardless of
the value of Day.
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