bitwise operators

This is a discussion on bitwise operators within the C Programming forums, part of the General Programming Boards category; Can someone explain to me bitwise operators please? I just dont seem to get it. Thanx ps. Can you explain ...

  1. #1
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    Question bitwise operators

    Can someone explain to me bitwise operators please? I just dont seem to get it.
    Thanx
    ps. Can you explain it to me as if I was an idiot?

  2. #2
    Skunkmeister Stoned_Coder's Avatar
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    I explained these before on the old board but after just going looking for the thread the search came up with nowt so i'll explain them again....

    ones complement operator ~
    This just reverses a bit.....
    so 0 becomes 1 and 1 becomes 0

    shift right operator >>
    this shifts all the bits 1 place to the right.The most significant bit becomes a zero as there isn't anything to shift in. This is a quick way of dividing integers by powers of 2.

    shift left operator <<
    This is the opposite of shifting to the right so this time the least significant bit is replaced by a zero and all other bits get shifted 1 place to the left.A quick way of multiplying integers by a power of 2.

    bitwise and &
    This is used mainly for clearing bits ( because anything anded with 0 is 0). It has the following truth table:-
    a b a&b
    0 0 0
    0 1 0
    1 0 0
    1 1 1

    bitwise or |
    This is used mainly for setting bits (because anything ored with 1 is 1).It has the following truth table:-
    a b a|b
    0 0 0
    0 1 1
    1 0 1
    1 1 1

    bitwise xor ^
    This is very similar to or except it doesn't produce a true result if both of its operands are true.It has this truth table.
    a b a^b
    0 0 0
    0 1 1
    1 0 1
    1 1 0

    here is a small code sample to print in binary...It shows how some of these operators are used.
    Code:
    #include<stdio.h>
    
    
    
    void printbits(unsigned int tobeprinted)
    {
    unsigned int shift=8*sizeof(unsigned int)-1; // bits are 0-31 not 1-32
    unsigned int mask=1<<shift;
    printf("%i is ",tobeprinted);
    for(unsigned int i=1;i<=(shift+1);i++)
    {
    
    if(tobeprinted &mask) printf("1");
    else
    printf("0");
    tobeprinted <<= 1;
    if (i%8==0) printf(" ");
    }
    }
    
    int main()
    {
    for (int i=1;i<10;i++)
    {
    printf("Enter positive integer :-");
    unsigned int input;
    scanf("%i",&input);
    printbits(input);
    printf("\n");
    }
    return 0;
    }
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

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