ok i am just a beginner in c.. i have the following prog. #include int main(){ int x,y,z; x=y=z=1; z = ++x || ++y && ++z; printf("x=%d y=%d z=%d ",x,y,z); return 0; } the output is 2,1,1 why is x being incremented at all? i mean the increment of x,y,z is for evaluation of z only, isnt it? shouldnt the output be 1,1,1? because we already defined the values of x and y, and later calculated z?

Question

ok i am just a beginner in c..
i have the following prog.
#include<stdio.h>
int main(){
  int x,y,z;
  x=y=z=1;
  z = ++x || ++y && ++z;
  printf("x=%d y=%d z=%d
",x,y,z);
  return 0;
}

the output is 2,1,1
why is x being incremented at all?
i mean the increment of x,y,z is for evaluation of z only, isnt it?
shouldnt the output be 1,1,1? because we already defined the values of x and y, and later calculated z?

yrelhan4 · Answer

@ganeshie8

e.mccormick · Answer

Look at your order of operations/evaluations/precedence. In what order is this evaluated? z = ++x || ++y && ++z; This is from Microsoft, but it is basically the same for any C you will run into. http://msdn.microsoft.com/en-us/library/2bxt6kc4.aspx

yrelhan4 · Answer

The and operator is evaluated first, and then the or operator. Yeah?

e.mccormick · Answer

And the ++ fires before both of them, but when it comes to the and/or, they are left to right.  So because ++x is true, the other side is NEVER evaluated.

e.mccormick · Answer

z = ++x || ++y && ++z; goes into the program as:

z = OK, we will assign something to z.

++x Increment this!

x || That is true, stop evaluating the right.

Therefore:
z = (incremented)x

Should be all it does.

e.mccormick · Answer

And yes, by that logic, it should be 212.  Not sure why it is 211.

yrelhan4 · Answer

Thank you so much. I get it.
And i think i know the answer to that part.
We are using logical operators here to evaluate z. So the answer can only be 0 or 1(false or true). As 2 || anything is always true.. so we get 1 for z.

e.mccormick · Answer

DOH!  Yah, I forgot that.  LOL.

e.mccormick · Answer

Which is why many programmers do increments on separate lines. It makes things cleaner. 

There, that fixed it.

yrelhan4 · Answer

We have tests having questions like these. And i am like, man i can write this in a better way. But yeah, it kinda improves the logic.
Thank you again. :)

e.mccormick · Answer

Yes, usually the point is to see the twisted order of how C does things.  I think those tests are why many programmers do some things on separate lines!