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#1 prannoy  Icon User is offline

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please explain this TC++ output

Posted 01 April 2007 - 03:31 AM

this is a code which i met by. The question is to find the output. but the one i got by myself had little resemblence with that given by the computer. i asked my teacher my friends. but none of them could give a sensible reason. i reckon there could be some wierd rearrangement or precedence rules in Turbo C++ which i am not aware of.

plz give it a try. and dont forget to post some replies.

the code is:
void main()
{ int x[]= {10,20,30,40};
int *p,*t,**q;
cout <<*p<<'\t'<<**q<<'\t'<<*t++;

so got 10 20 20 eh?

but sorry , the computer gives me
10 30 20

thanx for posting a reply!!

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Replies To: please explain this TC++ output

#2 horace  Icon User is offline

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Re: please explain this TC++ output

Posted 01 April 2007 - 03:48 AM

the probelm is you do not know when the ++ operator in the expression *t++ takes effect. In addition to evaluating the expression *t, the value of the variable in memory is altered (this is called a side effect). However, you do not know when this is done - it may be immediatly after evaluating *t or it may be saved until the next sequence point (in this case the ; ).
Thus it may be after the expression **q is evaluated and
you get
10 20 20
or before and you get
10 30 20

In practice do not use a variable more than once in an expression if one (or more) of the references has ++ or -- operators attached to it. You will get different results with different compilers.
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