Binary Format and 2's Complement Question

This is a discussion on Binary Format and 2's Complement Question within the C Programming forums, part of the General Programming Boards category; I've got an assignment to write a program that takes a decimal, and prints it's binary format, the 1's complement ...

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    Binary Format and 2's Complement Question

    I've got an assignment to write a program that takes a decimal, and prints it's binary format, the 1's complement of the binary format, and the 2's complement of the binary format.

    So far I've come up with the following solution:

    Code:
    #include "stdafx.h"
    #include "conio.h"
    #include "math.h"
    
    
    int _tmain(int argc, _TCHAR* argv[])
    {
        int n, k, c;
        printf("Enter an integer in decimal number system\n");
        scanf("%d", &n);
     
    
        printf("%d in binary number system is:\n", n);
     
        for (c = 31; c >= 0; c--)
        {
            k = n >> c;
            if (k & 1)
                printf("1");
            else
                printf("0");
        }    
    
        printf("\n\n");
    
        printf("%d's complement is:\n", n);
    
        for (c = 31; c >= 0; c--)
        {
            k = n >> c;
            if (k & 1)
                printf("0");
            else
                printf("1");
        }    
    
        _getch();
        return 0;
    }
    This way the binary conversion is working, but it starts the number with a bunch of 0s, based on c's value. And because of this, the complement will include a bunch of 1's that are not needed. Moreover, I have absolutely no idea how it'd be possible to add +1 to the created number, so that we get the 2's complement.

    Could you please help me with this, I'm sure there's a better way to start the whole process, but I could only find alternatives based on functions, and we haven't learned about those yet.

    Thanks very much!

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    Quote Originally Posted by sackboy127 View Post
    This way the binary conversion is working, but it starts the number with a bunch of 0s, based on c's value. And because of this, the complement will include a bunch of 1's that are not needed.
    I think you have to study how one's complement works. The 1's at the beginning are important.

    Bye, Andreas

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    Yes, I've come up with a solution that I think takes that into consideration as well. Basically, after scanning a number, I create 2 variables, the first one is "~number", and the second is "~number + 1". This way I create the complements while in decimal format, and convert each of the 3 into binary one by one. So far it seems to be working.

  4. #4
    Algorithm Dissector iMalc's Avatar
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    The real challenge here is to do it in a portable manner.
    I.e. print the two's-complement correctly when compiled on a one's-complement system and vice versa, as well as getting rid of that magic number 31 etc.
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