logic operators

[ashfire]

int main()
{
int x, y, z, q;
x = y = z = 1;
q = ++x || ++y && ++z; PRINT3 (x, y, z, q);
/* x=2 y=1 z=1 q=1*/

can someone explain to me whats going on here, i dont understand the logic and why some variables are being increamented and others are not

[CommonTater]

Good lord... If I ever write code like that please shoot me!

First off the logic operators are all wrong.

| is binary OR as in 1 | 0 = 1
|| is logical or as in this or that.

The same with the & ...
& is binary AND as in 1 & 1 = 1
&& is logical and as in this and that.

PRINT3 is not a C function so it must be defined someplace.

++ x | ++y & ++z would amount to 2 OR 2 AND 2 ... which has no choice but to equal 2

The code, as posted, makes no sense to me at all.

[ashfire]

i got this in a test

[CommonTater]

i got this in a test

Ouch.

[ashfire]

now you know how i feel about this i totally flunked the test apparently the commented values are the results of the logical operations

[ashfire]

#define PRINT3(x,y,z,q) printf("x=%d\ty=%d\tz=%d\tq=%d\n",x,y,z,q)

[Char*Pntr]

i got this in a test

I almost fainted when I saw your code. I waited for someone else to comment
first, fearing that maybe I'm drunk or off my rocker.

My only input is this:

main should be declared an int, and return an int upon successful
completion:

int main(void)
{  
       code here

return 0;

}

[ashfire]

ok let me put the whole test
insert

#include <stdio.h>
#define PRINT3(x,y,z,q) printf("x=%d\ty=%d\tz=%d\tq=%d\n",x,y,z,q)
int main()
{
int x, y, z, q;
x = y = z = 1;
q = ++x || ++y && ++z; PRINT3 (x, y, z, q);
/* x=2 y=1 z=1 q=1 since the expression is equivalent to
++x || (++y && ++z); */
x = y = z = 1;
q = ++x && ++y || ++z; PRINT3 (x, y, z, q);
/* x=2 y=2 z=1 q=1 since the expression is equivalent to
(++x && ++y) || ++z; */
x = y = z = 1;
q = ++x && ++y && ++z; PRINT3 (x, y, z, q);
/* x=2 y=2 z=2 q=1 */
x = y = z = 1;
q = ++x || ++y || ++z; PRINT3 (x, y, z, q);
/* x=2 y=1 y=1 q=1 */
x = y = z = 0;
q = ++x && ++y || ++z; PRINT3 (x, y, z, q);
/* x=1 y=1 z=0 q=1 */
x = y = z = 0;
q = ++x || ++y && ++z; PRINT3 (x, y, z, q);
/* x=1 y=0 z=0 q=1 */
x = y = z = 0;
q = ++x && ++y && ++z; PRINT3 (x, y, z, q);
/* x=1 y=1 z=1 q=1 */
x = y = z = 0;
q = ++x || ++y || ++z; PRINT3 (x, y, z, q);
/* x=1 y=0 z=0 q=1 */
x = y = z = -1;
q = ++x && ++y || ++z; PRINT3 (x, y, z, q);
/* x=0 y=-1 z=0 q=0 */
x = y = z = -1;
q = ++x || ++y && ++z; PRINT3 (x, y, z, q);
/* x=0 y=0 z=-1 q=0 */
x = y = z = -1;
q = ++x && ++y && ++z; PRINT3 (x, y, z, q);
/* x=0 y=-1 z=-1 q=0 */
x = y = z = -1;
q = ++x || ++y || ++z; PRINT3 (x, y, z, q);
/* x=0 y=0 z=0 q=0 */
return 0;
}

hell on earth

[jimblumberg]

This could be a part of the problem Sequence point - Wikipedia, the free encyclopedia

[CommonTater]

I almost fainted when I saw your code. I waited for someone else to comment
first, fearing that maybe I'm drunk or off my rocker.

I know the feeling... and I don't drink alcohol.

EDIT: The really scary part is that it compiles and runs, giving the answers shown...

[laserlight]

can someone explain to me whats going on here, i dont understand the logic and why some variables are being increamented and others are not

Among other things, this question tests whether you understand the short-circuit behaviour of || and &&. Now, ++x evaluates to 2, which evaluates to true, hence the left hand side of the || evaluates to true. Since this is sufficient to determine the result of the entire || expression, evaluation stops here, hence y and z are not incremented. Furthermore, the result of the expression is 1 (i.e., the "canonical" true value), hence 1 is assigned to q.

First off the logic operators are all wrong.

No, if the bitwise operators were used, there would not be this short-circuit/lazy evaluation.

[Char*Pntr]

I know the feeling... and I don't drink alcohol.

EDIT: The really scary part is that it compiles and runs, giving the answers shown...

Happy Halloween!

[CommonTater]

laserlight... If you understand this, how about picking a couple of lines and giving me a walk through... I have to admit this one just baffles me...

[CommonTater]

Happy Halloween!

LOL....

[laserlight]

laserlight... If you understand this, how about picking a couple of lines and giving me a walk through... I have to admit this one just baffles me...

I already went through ashfire's original question
If you want another one, examine:

x = y = z = -1;
q = ++x || ++y && ++z; PRINT3 (x, y, z, q);

Now, ++x evaluates to 0, but this is not enough to determine the result of the || expression, so ++y && ++z is evaluated. ++y evaluates to 0, and this is enough to determine that the result of the && expression is 0, so evaluation stops here, meaning that ++z is not evaluated (thus z remains as -1). The result of the expression is 0, so 0 is assigned to q. This is how we get:

/* x=0 y=0 z=-1 q=0 */