Increment / Decrement Operators - Help

This is a discussion on Increment / Decrement Operators - Help within the C Programming forums, part of the General Programming Boards category; Hi All, I have an small doubt in using Increment / Decrement operators.... Program is : Code: 1) #include<stdio.h> 2) ...

  1. #1
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    Exclamation Increment / Decrement Operators - Help

    Hi All,


    I have an small doubt in using Increment / Decrement operators....

    Program is :
    Code:
    1)   #include<stdio.h>
    2)   main()
    3)  {
    4)     int i=10;
    5)     printf("\nValue of I is :%d",++(--i));
    6)     getch();
    7)  }
    Compilation Error:
    at line 5, Error prompting stating "L value required".

    Is the syntax wrong or the usage of the Increment / Decrement operators is worng....

    Best Regards,
    Shyamlal SVS.

  2. #2
    Mad OnionKnight's Avatar
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    The usage is wrong, incrementing and decrementing returns an R value.

  3. #3
    Just kidding.... fnoyan's Avatar
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    Since the incrementing and recrementing are implemented as single assembly instructions(inc/dec), you cannot use them at the same time. Also, ++(i-2) will not work!

    See the assembly output of an increment statement.

    Code:
            movl    $10, -4(%ebp) <-- i=10
            leal    -4(%ebp), %eax 
            incl    (%eax)  <-- here is the i++

  4. #4
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    Code:
    The usage is wrong, incrementing and decrementing returns an R value.
    Cud u explain me what is R value?????

  5. #5
    Bond sunnypalsingh's Avatar
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    Quote Originally Posted by shyam168
    Cud u explain me what is R value?????
    L-values are values that have addresses, meaning they are variables or dereferenced references to a certain place.
    R-value is either l-value or non-l-value a term only used to distinguish from l-value.

  6. #6
    Yes, my avatar is stolen anonytmouse's Avatar
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    An l-value is a value that can be used on the left side of an assigment operator. An r-value is a value that can be used on the right side of an assignment operator:
    Code:
    l-value = r-value;
    Code:
    ++(--i)
    The expression highlighted in red yields the value 9. Obviously, this can not be used as as an l-value.

    The ++ operator, highlighted in blue, requires an l-value because it assigns a value to the value it is used on. Trying to use it on the value 9 would look like this:
    Code:
    /* 9 is not an l-value. This code won't work. */
    9 = 9 + 1;

  7. #7
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    Thanks to one and all forn clearing my doubt.....


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