Fundamentals of Programming: Boolean operators

You might have already covered a lot of boolean logic in Unit 2. Boolean logic is essential for anyone wanting to program. For example, you will end a game if it is true that the time is up.

if timeup = true then
  blowwhistle()
end if

We might want to use more complex boolean logic, for example if the time is 16:00 or before 9:00, it is the holiday or it is the weekend, then you don't have to go to school:

dim holiday, weekend as boolean
'...
If now > 16 OR now < 9 OR holiday OR weekend Then
  noschool()
Else
  gettoclass()
End If

Notice here how we didn't say, holiday = true, we just said holiday , if something is true, then comparing it to true will also return true (phew!), so there really is no need check and see. Programming languages allow you to compare boolean values using a variety boolean operators that you probably know and love:

$P$	$Q$	NOT	AND	OR	XOR
T	T	F	T	T	F
T	F	F	F	T	T
F	T	T	F	T	T
F	F	T	F	F	F

If you have been writing a lot of truth tables (you have Wittgenstein to blame), get VB.NET to do if for you!

console.writeline("A|B||A.B|A+B|AxB")'write the heading
for A = 0 to 1
  for B = 0 to 1
     console.write(A & "|" & B & "||") 
     console.write(A AND B & "|") 
     console.write(A OR B & "|") 
     console.write(A XOR B & "|")
     console.writeline()
  next
next

Exercise: Boolean Operators Answer: Answer: Answer:

for A = 0 to 1
  for B = 0 to 1
    for C = 0 to 1
       console.write(A & "|" & B & "|" & C & " = ") 'write the heading
       console.write(A AND B AND C & "|") 
       console.write(A AND B OR C & "|") 
       console.write(A OR B AND C & "|")
       console.write(A OR B OR C & "|")
       console.writeline()
    next
  next
next