post fix and pre fix operator simple puzzle

[anirudh]

hello everyone..
i have come across this very simple puzzle ..
consider
x=++a * --a * a++;
where the value of a=6..
what should be the value of X.
please give u r answers as well as u r solutions.. please.
thanks in advance.

[Banfa]

X could be anything and in fact and program invoking this code could do anything because this line invokes undefined behaviour because you have read and written the variable a more than once between sequence points.

[jessy]

what a very nice puzzle .........

i'm confused !! why is --a acting this way

i've tried a=2

the result should be X=3*1*2 = 6 but the result is 12 which means that he didn't decrement a so why the hell is that !!!!!!

plz answer me

[naeemulhaq]

Its simple.
Pre-fix operations are executed before the statement in which they occur and post-fix after that statement.

initially a = 6;
a = 6;
//++a makes a = 7
//--a makes a = 6

//so here you are doing: x = a*a*a
x= ( (++a * --a) * a++);

//here a becomes 7 due to a++

This program in calculating cube of a. I'm using Dev-C++.

[jessy]

could you please tell me how --a makes a =6 shouldn't it supposed to be 5

i tried a program that accepts an int from the user ( a) and output --a the result was 5 not 6 .......??
'
so if a=2 (++A*--A*A++)
= 3*1*2=6

and also i need to know what's DEV_c ?? that you are using ???

[vninja]

it should be 5 but since its the same variable consider:

x=++a*--a*a++;
since your incrimenting and decrimenting it becomes the original value

prstatement
a=6

first (++a)
a=7
secont pre(--a)
a=6
no more pre means do the statement
x=6*6*6
x=216
post fix (a++)
a = 7

[vninja]

it might depend on the program/compiler as well

for the two
the way it would be 12 and not 6 would be because it incriments and decrements the prefix before it uses the value and not the statement; ie

a=2

x=++a*--a*a++
it would incriment a to 3 first
then a =3 and not 2!!!!
producing 3*2
then since we postfix a is changed after use
making the expression x=3*2*2=12 and not x=3*1*2