示例：

/**
 *  @brief how about recursive-forward-1? show you here.
 *  @author wen`xuanpei
 *  @email 15873152445@163.com(query for any question here)
 */
#define _CRT_SECURE_NO_WARNINGS//support c-library in Microsoft-Visual-Studio
#include <stdio.h>

static char *uint2rstr_nonzero(char *str, unsigned int ui){
    if(ui){
        *str++ = ui % 10 + '0';
        return uint2rstr_nonzero(str, ui / 10);
    }
    return str;
}
static char * uint2rstr(char *str, unsigned int ui){
    if( !ui )
        *str++ = '0';
    else
        str = uint2rstr_nonzero(str, ui);
    *str = '\0';
    return str;
}

int main(){
    char str[20] = {};
    char *pt = NULL;
    pt = uint2rstr(str, 123U), printf("'%s', %d\n", str, pt - str);
    pt = uint2rstr(str, 0U), printf("'%s', %d\n", str, pt - str);
    getchar();
    return 0;
}

1）编译运行

2）要点分析

        1）在每一次函数调用层次增加之前做处理

        2）每一次处理，取得尾巴数字，输出到字符数组，从而得到逆序的字符串数字

尾声：

       其它不明白的地方不用过于纠结，那只是在浪费时间。学得多了，回过头来看自然融会贯通。