寻找符合规定的数

任意给定一个自然数N，寻找一个M，要求M是N的倍数，且它的所有位数都是0或1组成并要求M尽量小。

例：N＝3 M＝3＊37＝111

N＝31 M＝31＊3581＝111011

#include <stdio.h>

/* This function is used to add 1 to binary number of n. num[0] is high bit,
 * num[8] is low bit*/
void b_add(int num[])
{
    int i = 8;
    while (++num[i] == 2) {
        num[i] = 0;
        i--;
    }
}
/* This function is used to convert the binary number to decimal number.
 * exp.num[0] ~ num[5] is 0, num[6] ~ num[8] is 1, then the decimal 
 * number is 111*/
int b_to_d(int num[])
{
    int d_num, i;
    for (d_num = 0, i = 0; i < 9; i++) {
        d_num *= 10;
        d_num += num[i];
    }
    return d_num;
}
int main()
{
    int n, m;
    int binary_num[9];
    
    while (1) {
        printf("Please input a number or input ctrl + c to quit: \n");
        scanf("%d", &n);
        printf("The number qualified: \n");

        int i;
        for (i = 0; i < 9; i++) //init the binary_num to 000000000
            binary_num[i] = 0;
        do {
            b_add(binary_num);
            if ((m = b_to_d(binary_num)) % n == 0)
                printf("%d\n", m);
        } while(m < 111111111);
    }
    return 0;
}

这段代码可以统计九位数字内符合要求的数字，测试如图：