Some Basic questions

This is a discussion on Some Basic questions within the C Programming forums, part of the General Programming Boards category; Code: Operators Associativity () [] -> . left to right ! ~ ++ -- + - * (type) sizeof right ...

  1. #1
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    Some Basic questions

    Code:
    Operators 	                                           Associativity 
    
    () [] -> .	                                                   left to right
    ! ~ ++ -- + - * (type) sizeof	                       right to left
    * / % 	                                                       left to right
    + - 	                                                           left to right

    I was reading the 2nd chapter of K&R's The C programming language and came up accross this table.What i mentioned above is just a part of it.

    I was confused by the 2nd ,3rd and 4th rows. As we can see in the second we have +-*
    and in the 3rd we have * and in the 4th +-. Why the same thing is shown in different rows? Why is their Associativity different ?
    And what is meant by associativity.Is it that if the same operator is available in the same expression ?

    As i continued reading i came upon

    x = f() + g();

    where it said that the result is unpredictable.But wouldnt it go from left to right ? It should first it calculates the f() and then g() ... ?

    Im confused with all of these ... Any help would be great .Thank you

  2. #2
    spurious conceit MK27's Avatar
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    Quote Originally Posted by BlaX View Post
    I was confused by the 2nd ,3rd and 4th rows.
    The 2nd row are the unary operators, which form an expression with only one other element. This includes post/pre-increment (eg, i++ or --i). So that's different than the math operators + and - in line 4. Unary * is dereference, not multiply.

    The math operators are "binary", ie, they need two other elements to form an expression.
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  3. #3
    C++ Witch laserlight's Avatar
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    The result may well be predictable, but whether f() is evaluated first or g() is evaluated first is not predictable given just the source code.
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    DESTINY BEN10's Avatar
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    So here goes my doubt. How's the +,- of 2nd row different from +,- of the 4th row. Can anybody give an example where they are different. How can +,- be used as unary operators?
    HOPE YOU UNDERSTAND.......

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  5. #5
    and the hat of wrongness Salem's Avatar
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    a = -1;
    Unary minus

    a = +1;
    Unary plus
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  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by BEN10
    How can +,- be used as unary operators?
    By definition of "unary operator" and "left to right" associativity: +x and -x are such examples.
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  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Or, even better:
    a = -b; /* unary minus */
    etc.

  8. #8
    DESTINY BEN10's Avatar
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    Ok, thanks to all. Now I got it.
    HOPE YOU UNDERSTAND.......

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