c语言中输出十进制转换为二进制结果并指定显示的位数

#include <stdio.h>

int count_bits(unsigned x)
{
    int bits = 0;
    while(x)
    {
        if(x & 1U)
            bits++;
        x >>= 1;
    }
    return bits;
}

int int_bits(void)
{
    return count_bits(~0U);
}

int print_bits(unsigned x, unsigned n)
{
    int i = int_bits();
    i = (n < i) ? n - 1 : i - 1;
    for(i; i >= 0; i--)
    {
        putchar((x >> i & 1U) ? ‘1‘ : ‘0‘);
    }
    putchar(‘\n‘);
}

int main(void)
{
    unsigned a, b;
    puts("please input two nonnegative integers.");
    printf("a = "); scanf("%u", &a);
    printf("b = "); scanf("%u", &b);
    unsigned x;
    puts("please input the units to show.");
    printf("x  = "); scanf("%u", &x);
    
    printf("binary  a  =  "); print_bits(a, x);
    printf("binary  b  =  "); print_bits(b, x);
    
    return 0;
}

}