初步實現無循環（則遞歸）將任意整數轉任意進制字符串

不用循環的算法可以尋求遞歸來實現。

對於這個最大整數轉爲二進制時遞歸最深，64位64倍固定棧大小？。

itoa將num按radix進制轉換字符串到rec_array緩衝區，其中緩衝區未檢測。

#include"stdio.h"
#include"string.h"

int trace_counter = 0;
char *trace_array;
char *rec_itoa(int num, char *rec_array, int radix);

char *itoa(int num, char *array, int radix)
{
    char *rec_array = array;
    trace_array = array;        // trace
    if (num < 0)
    {
        num = -num;
        *array = '-';
        rec_array++;
        trace_counter++;        // trace
    }
    else if (num == 0)
        *array = 0 - '0';
    rec_array = rec_itoa(num, rec_array, radix);
    *rec_array = 0;
    return array;
}

char *rec_itoa(int num, char *rec_array, int radix)
{
    static char array_0_z[] = "0123456789abcdefghijklmnopqrstuvwxyz";
    printf("trace num : %d. \n", num);
    if (num >= radix)
    {
        rec_array = rec_itoa(num / radix, rec_array, radix);
        num %= radix;
    }

    *rec_array = array_0_z[num];

    printf("trace_%d: updata array[%d] = %c, now array = '%*s'\n", trace_counter, rec_array - trace_array, *rec_array, trace_counter + 1, trace_array);    // trace;

    trace_counter++;            // trace
    return ++rec_array;
}

// return buf+1 to change the pointer buf instead of moving it in a recursive <span style="font-family: Arial, Helvetica, sans-serif;">char *rec(char **buf, int len); will change buf.</span>
// function.
char *rec(char *buf, int len)
{
    if (len)
        buf = rec(buf, len - 1);
    printf("rec %s\n", buf++);
    return buf;
}

void rec_to_change_buf_is_na(char *buf, int len)
{
    // codes here are the same to the above but the last line;
}

int main()
{
    char buf[100] = "++++++++";
    printf("result: %s\n", itoa(244, buf, 2));
    char rec_buf[] = "201308021926";
    rec(rec_buf, strlen(rec_buf));

    //char * p= "abcde";
     //int a = (++p)++;
     //printf("a = %d\n", a);

     int *p[6], (*p2)[4];
     int arr[6][4];
     printf("\narr = %p,  arr[0] = %p\n", arr,arr[0]);
     p[0] = arr[0];
     p2 = arr;
     p2++;
     printf("p = %p,  p2 = %p\n\n%d\n",p, p2, 2^3);


}


/*
   ouptput :
   trace num : 244.
   trace num : 122.
   trace num : 61.
   trace num : 30.
   trace num : 15.
   trace num : 7.
   trace num : 3.
   trace num : 1.
   trace_0: updata array[0] = 1, now array = '1+++++++'
   trace_1: updata array[1] = 1, now array = '11++++++'
   trace_2: updata array[2] = 1, now array = '111+++++'
   trace_3: updata array[3] = 1, now array = '1111++++'
   trace_4: updata array[4] = 0, now array = '11110+++'
   trace_5: updata array[5] = 1, now array = '111101++'
   trace_6: updata array[6] = 0, now
   array = '1111010+'
   trace_7: updata array[7] = 0, now array = '11110100'
   result: 11110100
   rec 201308021926
   rec 01308021926
   rec 1308021926
   rec 308021926
   rec 08021926
   rec 8021926
   rec 021926
   rec 21926
   rec 1926
   rec 926
   rec 26
   rec 6
   rec