weird code line
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Thread: weird code line

  1. #1
    Member
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    Sep 2003
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    weird code line

    Was looking at some C++ code and saw a line of code that appeared a little bit weird. Wonder if someone around could have an idea, mdy is a variable:


    y = (mdy>>9) && 0x7f + 1900;


    this is part of a simple code that calculates julian dates out of our calendar and the date is introduced as a string variable, ie: 02121987 (february 12 1987)
    I Speak in frequencies even dogs have trouble hearing


  2. #2
    Custom User
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    I'm not incredibly sure how that works, but the >> is a binary shift right AFAIK and && is the and operator. I believe that when you use && like that it compares each bit and ands it, but I could be wrong.

    Doubt that really helps you understand what it's doing though. Worth a try

    ac

  3. #3
    AntiOnline n00b
    Join Date
    Feb 2004
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    665
    Hi

    Yes my friend Gothic said it ....They are called Bitwise Operators.....because they operate on individual bits.......

    Operator Meaning

    ~ :::::: One's Compliment

    >>:::::: Right Shift

    <<:::::: Left Shift

    & :::::: Bitwise "AND"

    | :::::: Bitwise OR

    ^ :::::: Bitwise XOR



    Can we have the whole code please.......

    until then Lest see what this code here does..it's performing some operation on the year part of the date(my interpretation of the code i could be wrong) ..........

    y = (mdy>>9) && 0x7f + 1900;

    this would be evaluated as ((mdy>>9) && 0x7f) + 1900 so i will maintaiin the sequence

    mdy>>9

    This would Shift all the bits in mdy nine places to the right

    for e.g. if mdy=11010111
    then mdy>>1 =01101011
    Similarly mdy>>2=00110101

    I belive by right shift what ists trying to do is get the Year out of the variable mdy(month day Year)

    it should be something like this

    Code:
    
    0  0   0   1   0  1   0    0    0    1   1   0    1     0    0   1      
    
    |<------- Year-------->|<-----Month----->|<---------day---------->|
    
    If we right Shift By 9 we Get the Yesr
    
    0  0   0   0   0  0   0    0    0    0   0   0    1     0    1   0      
    
                                              |<--------Year-------->|
    
    


    &&0x7f

    "I believe that when you use && like that it compares each bit and ands it, but I could be wrong."

    "&&" is a Logical "AND" operator Not Bitwise.......i am not sure if it would be evaluated as the bitwise operator "&"..i will check it as soon as get my hands on a C++ compiler........

    ok made a small program to test that and Gothic sorry but you seem to be wrong there from what i am getting......works in TurboC++ can't take responcibility or any other C++ compilers.......

    Code:
    #include<iostream.h>
    #include<conio.h>
    
    showbits(int);
    
    void main()
    {
    	int i,j,k;
    
    	k=9;
    	i=40;
    
    	clrscr();
    
    	showbits(i);
    	cout<<endl;
    	showbits(k);
    	cout<<endl;
    
    	j=i&k;
             //j=i&&k;
    	showbits(j);
    	cout<<endl;
    
    getch();
    }
    
    //This Function Will Print the Binary of any Integer 
    or Character that is Passed to it as the parameter.....
    showbits(int n)
    {
    	int i,k,andmask;
    
    	for(i=15;i>=0;i--)
    	{
    		andmask=1<<i;
    		k=n&andmask;
    
    		k==0?cout<<"0":cout<<"1";
    	}
    return;
    }
    
    Output
    
    case 1 ::   i & j 
    
    The Result :: i=0000000000101000
                  j=0000000000001001
                   -------------------
                    0000000000001000
    
    Case 2 :: i && j
    
    The Result :: i=0000000000101000
                  j=0000000000001001
                  --------------------
                    0000000000000001
    
    
    + 1900

    I don't think it needs any explaination..............

    -Good Luck--

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