Pascal Programming

George Boole, a 19th Century mathematician, is created with true, false logic.

A Boolean expression in Pascal will be true or false. Compound expressions are created with the

operators and, or, not. Since interlocking expressions –e g: a>b>c—are not

allowed in Pascal. So, Boolean expressions are combined to accomplish the same end result.

continue . . .

Pascal Programming

And . . . Expects this and that condition will both be met for the statement to be true.

Or . . .Expects that one or both conditions will be met for the statement to be true.

Not . . . Changes true to false and false to true. Precedence affects these operators– they are

settled (1) not, (2) and (3) or. continue . . .

Pascal Programming

An expression with and yields true only when both are true. If one or both conditions are false it yields false.

An expression with or yields true unless both conditions are false.

An expression with not yields true when the expression is not(true).

The Turbo compiler uses short-circuit evaluation—evaluating only as many conditions as may be needed to determine the value.

Pascal Programming

Using Sets . . . A Boolean can evaluate a set. Syntax . . .Ans in [‘A’, ‘B’] –in is a reserved

word. A Set contains a list of constants separated

by commas and enclosed in square brackets. The set may be used as a sub-part of a

Boolean expression. (Not precedes the expression.)

Pascal Programming

A variable can contain a Boolean expression but it must be type Boolean.

Variables with type Boolean are declared just like other variables.

A function can return a type Boolean. This can make it read more like natural language.

Pascal Programming

Multiway branching can be accomplished with nested if-then-else statements . . .

e g: if N > 25 then• If O > than 5 then

– . . . . . . . . or Case statements.

continue . . .

Pascal Programming

Syntax . . . (The Label List follows the of.)– Case Grade of

• ‘A’ , ‘B’: writeln(‘Very Good!’);• “C”: writeln (‘Passing’);• ‘D’, ‘F’: writeln (‘Too bad!’);• else• Writeln(‘No Grade was posted.’)• End

Case statements can be controlled by types integer or char but not real or string.

The else can be omitted with an effect similar to omitting it on the if-then-else statement.