在C Primer Plus （第6版）中文版 P224中程序清单9.8 binary.c程序，运行错误

Question

C Primer Plus （第6版）中文版 P224中程序清单9.8 binary.c程序，在运用递归实现二进制打印整数时，有一个错误
使用了未初始化的局部变量“r”，麻烦各位，怎么修改才不会有错误

#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_s("%lu", &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)
{
    int r;

    if (n >= 2)
        to_binary(n / 2);
    putchar(r == 0 ? '0' : '1');

    return;
}

Answer 1

修改如下：

#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("%lu", &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)
{
    int r = n%2;   //赋值就不会报错
    if (n >= 2)
        to_binary(n / 2);
    putchar(r == 0 ? '0' : '1');

    return;
}