Compound Boolean Expressions

And, Or, and Not: 3.5.1

• use &&to make 2 things true when evaluating boolean expressions
  • Logical and
  • condition will only evaluate true if both are true
  • Often used to see if a number is in a range
    • (score => 0 && score <= 100)
• use || if only one of two things has to be true
  • Logical or
  • This is inclusive
    • It will evaluate true if both things are true
  • Often used to check for error conditions with numerical values
    • (score < 0 || score > 100)
• ! can be used to negate a boolean value
  • Logical not
  • Used in !=
  • Reverses a boolean value
    • !false is true
• Order of operations is
  1. Parenthesis
  2. !
  3. &&
  4. ||

Truth Tables: 3.5.2

• Expressions involving logical operators evaluate to a boolean value

P && Q

P	Q	P && Q
true	true	true
false	true	false
true	false	false
false	false	false

P || Q

P	Q	**P		Q**
true	true	true
false	true	true
true	false	true
false	false	false

Short Circuit Evaluation: 3.5.3

• && and || use short circuit evaluation
  • The second expression isn’t always checked if the first is enough to evaluate an expression
  • expr1 || expr2
    • If expr1 is true, we don’t need to check expr2 to know the expression will be true
  • expr1 && expr2
    • If expr1 is false, we know the expression will be false regardless of what expr2 evaluates to

Truth Tables POGIL: 3.5.4

sunny	raining	temperature > 80	!raining && (sunny || temperature > 80)
false	false	false	false
true	false	false	true
true	true	false	false
true	true	true	false
true	false	true	true
false	false	true	true
false	true	false	false

Summary: 3.5.5

• Logical operators are used with boolean values
  • ! not
  • && and
  • || or
• (A && B) is true if both A and B are
• (A || B) is true if either A or B are
• !A is true if A is false
• Order of operations is ! -> && -> ||
• When the result of a logical expression using && or || can be evaluated with the first expression, the second is ignored
  • Known as short circuit evaluation