understanding the book

This is a discussion on understanding the book within the C Programming forums, part of the General Programming Boards category; I was just reading a C book, and came across this: Do not use increment, decrement, or compound assignment operators ...

  1. #1
    back? dbaryl's Avatar
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    understanding the book

    I was just reading a C book, and came across this:
    Do not use increment, decrement, or compound assignment operators as subexpressions in complex expressions.
    I'm having a hard time understanding the wording... would it be something like this?
    Code:
    //Don't do this:
    a = b + c++
    This is my signature. Remind me to change it.

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    ATH0 quzah's Avatar
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    Yeah, that's pretty much what they're saying. You don't want to use ++ / -- operators in complex expressions generally because you may confuse yourself on how soon they're incremented.

    Quzah.
    Hope is the first step on the road to disappointment.

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    Thanks, that was a quick response
    This is my signature. Remind me to change it.

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    And also not every compiler treats ++ and -- the same. So in a calculation like:

    a = i+++j;

    The result may not always be the same.

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    Code Goddess Prelude's Avatar
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    >because you may confuse yourself on how soon they're incremented.
    Or you could inadvertently invoke undefined behavior by modifying a variable more than once between sequence points. This is generally a hard one to spot.

    -Prelude
    My best code is written with the delete key.

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    TransparentMember correlcj's Avatar
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    Do not use increment, decrement, or compound assignment operators as subexpressions i

    From what i too have been studying is that eg; static const int k = 3;
    Yes you can initialize k but you can not assign nor ++ or -- it. Even though a variable has been qualified with const, it still cannoit be used to specify an array size in another declaration.
    Just a little FYI ...
    "Be formless, shapeless, like water... You put water into a cup, it becomes the cup, you put water into a bottle, it becomes the bottle, you put it in a teapot, it becomes the teapot... Now water can flow, or it can crash, be water my friend."
    -Bruce Lee

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    ATH0 quzah's Avatar
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    Re: Do not use increment, decrement, or compound assignment operators as subexpressio

    Originally posted by correlcj
    From what i too have been studying is that eg; static const int k = 3;
    Yes you can initialize k but you can not assign nor ++ or -- it.
    Of course you can't. You've declared it const. This goes without saying. You cannot modify a constant variable.

    As for your second part, I believe with the latest version of the standard you can. Then again, I've never bothered to read the standard, so I may be off there.

    Also, it depends on your compiler. For example, with gcc, you can do the following:

    Code:
    #include <stdio.h>
    int main ( void )
    {
        int x = 5;
        {
            char array[x]={0};
            int y;
            for( y = 0; y < x-1; y++ )
                array[y]='a'+y;
            printf("%s",array);
        }
        return 0;
    }
    And it will compile and execute.

    Quzah.
    Hope is the first step on the road to disappointment.

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