C使用联合将十进制数转换为二进制

Question

I have this code:

#include <stdio.h>
#include <string.h>
int main(void)
{
    long long int n,b,t,j;
    while(scanf("%llu",&n) && n)
    {
        char a[2000]={0},c[2000]={0};
        b=0;
        int k=0;

        while(n>0)
        {
            a[b++]=(n%2)+48;
            if(n%2==1)
            k++;
            n=n/2;
        }
            a[b]='\0';
            j=strlen(a)-1;

        for(b=j,t=0;b>=0;b--)

            c[t++]=a[b];
            c[t]='\0';

        printf("The parity of %s is %d (mod 2).\n",c,k);
    }

return 0;
}

This code working perfect.

Now I want to convert decimal number to binary using union in C

How can I do that?

Answer 1

You can't, that doesn't make any sense. Decimal and binary are representations of numbers. Ten cars in decimal is the same number of cars as ten cars in binary. It's precisely the same number. There's no way to use a union to change one integer representation to another.

Answer 2

Since the number is not represented in decimal in memory, you have already accomplished this task, without even using a union. If you want to obtain a binary textual representation:

unsigned n = 12345;

for (int i = sizeof(n) * CHAR_BIT - 1; i >= 0; i--) {
    putc('0' + ((n >> i) & 1), stdout);
}

Answer 3

Why?

A union is merely a structure where all the members have the same location in memory (they overlap).

I'm not familiar with any typical approach for using a union when creating a binary string, I don't think that's (easily) possible at all.

Perhaps you're confusing the use of unions when converting between floating point and integers (ugly but sometimes used to get at the bits for a floating point number)?

Answer 4

#include <stdio.h>
#include <conio.h>
union calc
{
    struct {
        unsigned char bit0  : 1;
        unsigned char bit1  : 1;
        unsigned char bit2  : 1;
        unsigned char bit3  : 1;
        unsigned char bit4  : 1;
        unsigned char bit5  : 1;
        unsigned char bit6  : 1;
        unsigned char bit7  : 1;
    } bits;
   unsigned char numero;
};  
int main(int argc, char *argv[]) {
    union calc  c;
    scanf("%u",&c.numero);
    printf("%d%d%d%d%d%d%d%d",c.bits.bit7,c.bits.bit6,c.bits.bit5,c.bits.bit4,c.bits.bit3,c.bits.bit2,c.bits.bit1,c.bits.bit0);
    getch();
    return 0;
}