Thread: Boolean Algebra

Boolean algebra works on two values: true or false. For values that aren't true or false (like 3) C++ "converts" it to true or false using the basic idea that 0 is false and everything else is true.

NOT says: take the boolean value and return the other boolean value. So true becomes false and false becomes true. Think about it in english: You are allowed to go see the movie. Vs: You are not allowed to go see the movie.

AND asks if two values are both true. So TRUE/TRUE is TRUE but TRUE/FALSE, FALSE/TRUE, and FALSE/FALSE are all FALSE. Jack and Jill both start with y is false.

OR asks if at least one of the two values are true. TRUE/TRUE, TRUE/FALSE, FALSE/TRUE are true but FALSE/FALSE is FALSE. This operator does lead to some confusion as English tends to imply that one of the values are true but the other is false (you can have the red pill or the blue pill). Logically this is actually an XOR (Exclusive OR) where only one of the values may be true. So TRUE/TRUE would be false.

let me got back and restudy that part of lesson 2 to see if I can figure out how they got the answer they got for the question in the quiz of that lesson.

You've heard of order of operations, right? Parentheses first, then look at what's outside.

man you just told me the same thing my sister said. so the reason

C. !( ( 1 || 0 ) && 0 ) ANSWER: 1 (Parenthesis are useful)

is because its 1 OR 0 evalutes to 1 then the outer parenthesis becomes !1 (which is really 0) !0 || 0 evaluates to 1 because both operands are NOT false so it gotta be true
but would it be done like this?

!( (1 OR 0 = 0) && 0 )
!( 0 && 0 = 0) so the statement become !0 so its 1. Right?

1 or 0 is 1. But 1 && 0 is still 0, so from then on it's right.

ok gotcha I typed that in wrong I was watching the Laker Magic Game lol Thank you to everyone who bothered to help me out.

hey I'm new here, I just started learning C++ and just want to say how helpful this thread has been. I was completely lost on lesson two as well but reading these replies has really helped me, so thanks everyone!

friends, I am new to C. here is problem, whose output I could not understand. could you please help me out?

Code:

main()
{
   int i=4,j=-1,k=0,w,x,y,z;

   w=i||j||k;
   x=i&&j&&k;
   y=i||j&&k;
   z=i&&j||k;


   printf("\nw=%d x=%d y=%d z=%d\n",w,x,y,z);
}

the output is w=1 x=0 y=1 z=1

I am confused why w=1 in the answer, when expression says w=4 or -1 or 0
similarly others?

thanks in advance

The logical operators OR and AND are short-circuiting. With OR that means stop when you find truth, and with AND it means stop when you find falsehood, because these results will end up being the results for the whole expression. If you evaluate any Boolean expression you will either find truth or falsehood.

The result of a Boolean expression also belongs in a bool. That way you can do things like

Code:

#include <iomanip>
#include <iostream>

std::cout << std::boolalpha << whatdoesitmean << std::endl;

and it makes a little more sense to the layperson.