/*以二进制形式输出整数*/#include <stdio.h>void to_binarry(unsigned long n);
int main (void ){    unsigned long number;    printf ("Enter an integer(q to quit):\n");    while (scanf("%ul",&number)==1)    {        printf("Binarry equivalent:");        to_binarry(number);        putchar('\n');        printf("Enter an integer (q to quit):\n");    }    printf("Done.\n");}void to_binarry(unsigned long n )//递归函数。{    int r;    r = n % 2;    if (n>=2)    {        to_binarry(n/2);
    }    putchar ('0'+ r );    return;

/*以二进制形式输出整数*/#include <stdio.h>void to_binarry(unsigned long n);int main (void ){    unsigned long number;    printf ("Enter an integer(q to quit):\n");    while (scanf("%ul",&number)==1)    {        printf("Binarry equivalent:");        to_binarry(number);        putchar('\n');        printf("Enter an integer (q to quit):\n");    }    printf("Done.\n");    return 0;}void to_binarry(unsigned long n )//递归函数。{    int r;    r = n % 2;    if (n>=2)    {        to_binarry(n/2);
    }    putchar ('0'+ r );    return;}

單獨執行一下這句看看就知道是什麽意思了唄

putchar（'0'+r）输出是没问题的，但就是不知道是什么意思？

仅在r是0-9的整数时是正确的，实际的意思是将单个整数数字转换成字符，你看看ASCII表就会明白，实际的运作是：putchar((char)((int)'0'+r));

明白了