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unary postfix operators

 
Timothy Sheehy
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Hi all,

I'm very confused by a simple section of code that is not giving expected results!



What should be printed out? I wuold say 5, but I am wrong.
I cannot figure out why!

A similar phenomenon happens with the postfix -- operator.

However:


This gives the expected result a = 7, b = 8

Can anyone shed any light on this?

Thanks!
 
Peter Chase
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Originally posted by Timothy Sheehy:



What should be printed out? I wuold say 5, but I am wrong.
I cannot figure out why!

The line "s = s++" does the following:

  • Get the value of the expression s++, which is 4
  • Increment s to 5
  • Assign the value of the expression to s, putting it back to 4


  • If it was "s = ++s", it would make s equal 5, though it would be an odd (inefficient) way to do it.
     
    Timothy Sheehy
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    Thanks Peter, I understand.

    I read it as the entire line must be evaluated before the post-increment.
    However, the expression of the right hand side of the = operator must be completely reduced before the asignment can be affected.

    The RHS is evaluate. The ++ is executed. The RHS has been reduced (to 4) and can now be used in the assignment.

    Thanks for the feedback. This has been troubling me for a couple of hours now.

    Cheers!
     
    Mahesh Bhatt
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    hi

    if your doubt is regarding the postfix and prefix operations . Try the following.
    keep in mind the variable "x" , and the "expression" , then as you solve the expression step by step .... keep in mind the golden rule :

    1) when its ++x , increment x and then assign the value of x in the expression .

    2) when its x++, first assign the value to the expression and then increment the value of x.

    ex : int x=0;
    int y= x++ + ++x +++y + y++;

    try solving this simple problem with keeping the golden rule on your "tounge" ...if u can solve this (please match the result you get with the result that the computer gives ) the ...u can solve any complex problem .
    [ September 16, 2004: Message edited by: prashant bhogvan ]
     
    Timothy Sheehy
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    That's a great trick.

    Thanks!
     
    Abhi Raj
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    The example as above will not compile as y has not been initialized. Need to do :

    int x=0;
    int y=0; //***initialize y first
    y = x++ + ++x + ++y + y++;

    I think it would make a good interview question
     
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