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Using the Logical OR

Operator

The logical OR operator, ||, lets you join two expressions to form a larger one, which can be evaluated to true or false. The new expression is true if the first

66 Chapter 2 n Truth, Branching, and the Game Loop: Guess My Number


expression or the second expression is true; otherwise, it is false. Just as in English, ormeans either. If either the first or second expression is true, then the new expression is true. (If both are true, then the larger expression is still true.) Heres a concrete example from the Designers Network program:

else if (username == "guest" || password == "guest")

The expression username == "guest" || password == "guest" is true if username == "guest" is true or if password == "guest" is true. This works perfectly because I want to grant a user access as a guest as long as he enters guest for the username or password. If the user enters guest for both, thats fine too.

Another way to understand how || works is to look at all of the possible combinations of truth and falsity (see Table 2.4).




image

true

true

true false

true

false

true false

true

true

false false

username == "guest" ||

password == "guest"

password ==

"guest"

username ==

"guest"

Table 2.4 Possible Login Combinations Using the OR Operator