decimal to binary and binary to 1's and 2's complement

/*****************************
 *  Umang B Bhatt            *
 *   bhatt.umang7@gmail.com  *
 *****************************/

/**
 * program for decinal to binanry and 1's and 2's complement
 */

#include<stdio.h>
#include <string.h>


void main()
{

    struct binary
    {
        int f : 2; // we use bit field here because it occupies less space

    } b[100], c[100], d[100];

    /**
     * b[] will store binary, c[] will store 1's complement
     * d[] will store 2's complement
     */
    /* a will store decomal*/
    long int a;
    long int n, i, j; // n is the length of binary. i and j are for loops.

    // now scanning pisitive number

    do
    {
        printf("\nEnter a valid positive integer number: ");
        scanf("%ld", &a);
    }

    while (a < 0);
    for (i = 0; a != 0; i++)
    {

        b[i].f = a % 2;
        a = a / 2;
    }

    n = i - 1;
    printf("\nBinary of entered number is: ");

    for (i = n; i >= 0; i--)
    {

        printf("%d", b[i].f);
    }
    /**
     * 2's complement of binary nyumber
     * binary        : 1 0 1 0 1 1 0
     * 2's complement: 0 1 0 1 0 1 0
     * while going right to left put 0 as it is untill you get 1. put 1 as it is
     * and then change 1 to 0 and 0 to 1.
     */
    for (i = 0; i <= n; i++)
    {

        if (b[i].f == 1)
        {
            d[i].f = 1;

            i++;
            for (j = i; j <= n; j++)
            {

                if (b[j].f == 1)
                {
                    d[j].f = 0;
                }

                else
                {
                    d[j].f = 1;
                }
            }

            break;
        }
        else
        {
            d[i].f = 0;
        }
    }

    printf("\n\n2's complement of number is: ");
    for (i = n; i >= 0; i--)
    {

        printf("%d", d[i].f);
    }

    /**
     * getting and printing 1's complement
     * binary         : 1 0 1 0 1 1 0
     * 1's complement : 0 1 0 1 0 0 1
     * this one is having simple logic. change all 0 to 1 and all
     * 1 to 0.
     */

    printf("\n\n1's complement of number is: ");
    for (i = n; i >= 0; i--)
    {

        if (b[i].f == 0)
        {
            c[i].f = 1;

            // if it is 0 then change to 1
        }
        else
        {
            c[i].f = 0;
        }

        printf("%d", c[i].f);
    }
    printf("\n");
}