下面是 程序
#include "stdafx.h"
void to_binary (unsigned long n);

int _tmain(int argc, _TCHAR* argv[])
{
unsigned long number;
printf("enter an integer (q to quit): \n");
while (scanf("%ul", &number) == 1)
{

printf("binary an integer (q to quit): \n");
to_binary (number);
putchar('\n');
printf("enter an integer (q to quit): \n");
}
printf("done. \n");
getchar();
getchar();
getchar();
return 0;
}

void to_binary (unsigned long n)
{

int r;
r = n % 2;
if (n >= 2)
to_binary (n / 2);
putchar ('0' + r);
}
红色部分的函数不是太明白 麻烦大家给 讲解下 谢谢！最好能把红色部分的步骤给写一下谢谢

/* binary.c -- prints integer in binary form */
#include <stdio.h>
void to_binary(unsigned long n);

int main(void)
{
    unsigned long number;
    printf("Enter an integer (q to quit):\n");
    while (scanf("%ul", &number) == 1)
    {
        printf("Binary equivalent: ");
        to_binary(number);
        putchar('\n');
        printf("Enter an integer (q to quit):\n");
    }
    printf("Done.\n");
  
   return 0;
}

void to_binary(unsigned long n)   /* recursive function */
{
    int r;

    r = n % 2;
    if (n >= 2)
       to_binary(n / 2);
    putchar('0' + r);
  
    return;
}
这是源代码