Newbie question !( 1 || 0 ) - ?

I was going through Lesson 2 in the tutorials. At the end, it has some statements ~

Code:

---

A. !( 1 || 0 )        ANSWER: 0       
B. !( 1 || 1 && 0 )    ANSWER: 0 (AND is evaluated before OR)
C. !( ( 1 || 0 ) && 0 )  ANSWER: 1 (Parenthesis are useful)

---

What does the ! do here?
How does 1 && 0 evaluate to 0? (previous paragraph in tutorial)

Thanks :D

! means not

for example:

Code:

---


a = 1;
if( a != 3 )
{
  cout << "blah Blah" << endl;
}


//OUTPUT:

blah blah

//because a  is not 3..

---

> How does 1 && 0 evaluate to 0?
How can something be true and false?

- SirCrono6

Quote:

---

Originally Posted by SirCrono6

> How does 1 && 0 evaluate to 0?
How can something be true and false?

- SirCrono6

---

Maybe I'm reading into it too much..

All I get from !(1 && 0) is "Not(True AND False)" I don't see how an answer can come from that :D

I understand If statments quite well :)

Hi,

AND requires both terms to be true for the result to be true, where OR only requires one term to be true for the result to be true. So, starting with the parentheses:

(True AND False)

you get:

(false)

because both terms aren't true. Then, NOT reverses the result, so

!(false)

gives you true.

If the problem had OR instead:

!(true OR false)

since OR only requires one term to be true for the result to be true, you would get:

!(true)

which is false.

Don't read too much into the names given to the logical operators ('and', 'or' ... especially 'or'). The meanings of these words in English does not completely correspond to their logical meanings, just take them as definitions.

p && q is true if and only if p is true and q is true
p || q is false if and only if p is false and q is false
!p is true if and only if p is false

Cheers

Ok, that makes sense now.. Thanks for clarifying :)

i'm sure you probably know, but i haven't seen anyone point this out, so i will. anything that evaluates to zero evaluates to false;
anything that evaluates to anything that's NOT zero, evaluates to true.

if you REALLY want to learn about logic operators, i suggest reading some ASM tutorials concerning bitwise operations.

just a little example of logic operators in it's binary form

Code:

---

1010
1000 &&
----------
1000  = true (not zero)  //  !1000 = false

1010
0100 ||
---------
1110  = true (not zero)  //  !1110 = false;


0101
0101 XOR //i forget the XOR operator in c/c++ (^ maybe?)
------------
0000  = false (zero)    //  !0000 = true;

for you specific question -

0001
0000 ||
------------
0001 true  // !0001 = 0000 = false

---

I dont think there is a XOR operator availible in c++..some people say its a flaw..hu knows..a quick and easy work around is:

bool p, q;

(p || q) && !(p && q)

producing an xclusive OR..

cheers

Alex

> I dont think there is a XOR operator availible in c++
Of course there is, and it's ^

is that quite a recent addition to c++?

becuase the book im reading says there isnt one..

man..i feel dumb!

thanx for the heads up!

cheers
Alex

> is that quite a recent addition to c++?
No, it's there from original C, which means it's been there forever basically.

Of course what Salem is failing to state is that it's bitwise XOR :)

bitwise?

Please explain further?

cheers
Alex

Quote:

---

Originally Posted by macman

bitwise?

Please explain further?

cheers
Alex

---

Bitwise:

00010001 XOR 00100001

00010001
00100001
-------------
00110000

Bitwise means that the XOR operator takes a look at the individual bits. XOR, in this case 'Exclusive OR', means that only one can be true to evaluate to true.

Does that help?

Yeh..i think ive got u there now Lithorien, thanx for the info..

so as far as I can gather..i was right in some ways but wrong in stating that there is no technical XOR operator!

KK..cool

cheers, and thanx again

Alex

Quote:

---

Originally Posted by Thantos

Of course what Salem is failing to state is that it's bitwise XOR :)

---

What other kind is there?

Logical....

Logical XOR doesn't exist in C++. Of course it's simple to implament

Quote:

---

Originally Posted by Thantos

Logical....

Logical XOR doesn't exist in C++. Of course it's simple to implament

---

I thought it was the same thing - i.e. that they were interchangable. I mean the following works:

Code:

---

if (i == 2 | j == 6)

---

...because you're applying bitwise logic to the conditions. I think it will even drop short-circuiting in this case (should you want to).

So you could apply logical XOR by the same token...

Bitwise and logical are not the same.

Take:

Code:

---

if ( 10 && 5 )

---

This is true

Code:

---

if ( 10 & 5 )

---

This is false

Obviously they aren't interchangeable.

Now when you get down to just boolean values they do become interchangeable but not until you get to that point.

Quote:

---

I think it will even drop short-circuiting in this case (should you want to).

---

AFAIK short-circuit evaluation is always done when possible

I meant with regards to conditions, so yes, Booleans only.

And I just tested it on my compiler (MSCV++ 6.0) - it doesn't do short circuiting at all!

sigh...

Code:

---

if ( 10 && 5 )

---

is a condition and it's valid. Conditions are not boolean only. They will resolved down to booleans but that doesn't mean it started with and only contains booleans.

Quote:

---

And I just tested it on my compiler (MSCV++ 6.0) - it doesn't do short circuiting at all!

---

Well what did you test?