Comment implémenter la conversion entre bases arbitraires en langage C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <windows.h>
#define N 50
//进制转换
char * Ten_MoreThanTen(int, int);   //10进制数转换成10以上进制数的函数

int MoreThanTen_Ten(int, char []);  //10以上进制数转换成10进制数的函数

int Ten_LessThanTen(int, int);    //10进制数转换成10以内进制数的函数

int LessThanTen_Ten(int, int);    //10以内进制数转换成10进制数的函数

char array[N] = "\0";   //全局变量，用于存储转换后并且倒置了的数据

int LessThanTen_Ten(int before, int num)   //10以内转换10，参数brfore为初始进制,num为初始数值
{
    double result = 0.0;             //转换成10进制后的结果
    int i = 0;
    for(i = 0; num != 0; i++)        //利用for循环实现按权展开相加
    {
        result += pow(before, i) * (num % 10);
        num /= 10;
    }
    return (int)result;  //返回值为转换后的结果
}

int Ten_LessThanTen(int after, int num)  //10转换10以内，参数after为转换后的进制，num为10进制数值
{
    double result = 0.0;            //double类型因为pow函数的返回值为double类型
    int i = 0;
    for(i = 0; num != 0; i++)       //利用for循环实现连续取余
    {
        result += (num % after) * pow(10, i);
        num /= after;
    }
    return (int)result;
}

int MoreThanTen_Ten(int before, char num[]) //10以上转换10
{
    int i = 0;
    double result = 0.0;
    int length = strlen(num);
    for(i = length - 1; i >= 0; i--)
    {
//利用ASCALL码将所有元素转换成对应的整型
        if(&#39;A&#39; <= num[i] && num[i] <= &#39;Z&#39;)
            result += pow(before, length - i - 1) * (num[i] - 55);
        else if(&#39;a&#39; <= num[i] && num[i] <= &#39;z&#39;)
            result += pow(before, length - i - 1) * (num[i] - 87);
        else if(&#39;0&#39; <= num[i] && num[i] <= &#39;9&#39;)
            result += pow(before, length - i - 1) * (num[i] - 48);
    }
    return (int)result;
}
char * Ten_MoreThanTen(int after, int num)   //10转换10以上
{
    int i = 0;
    int j = 0;
    int tmp = 0;    //存储每次余数的中间变量
    char tmp_array[N] = "\0";   //转换后未倒置的数组
    for(i = 0; num > 0; i++)
    {
        tmp = num % after;
        if(tmp < 10)   //对大于等于10的余数进行字母转换
            tmp_array[i] = tmp + &#39;0&#39;;
        else
            tmp_array[i] = tmp + &#39;A&#39; - 10;
        num /= after;
    }
    for(j = 0; i > 0; i--, j++)  //倒置
    {
        array[j] = tmp_array[i - 1];
        array[j + 1] = &#39;\0&#39;;
    }
    return array;   //输出转换后存储数据的字符串地址
}
int main()
{
    int before = 0;     //转换前的进制数
    int after = 0;      //转换后的进制数
    int num1 = 0;       //要转换的十进制以内的数
    char array_num1[N] = "\0"; //要转换的十进制以上的数
    int num2 = 0;       //转换之后的数
    char *str_num2;     //转换之后的数的地址
    int tmp_num1 = 0;   //判断输入是否合法时代替num1的中间变量
    int i = 0;
    int m = 0;  //计数器
    while(1)    //整个while语句用于录入以及判断输入是否合法
    {
        printf("初始进制：");
        scanf("%d", &before);
        printf("目标进制：");
        scanf("%d", &after);
        printf("初始数值：");
        if(before > 10) //通过对初始进制判断，决定
            scanf("%s", array_num1);
        else
            scanf("%d", &num1);
        for(i = 0, tmp_num1 = num1; tmp_num1 != 0; i++)
        {
            if((tmp_num1 % 10) <= before && tmp_num1 % 10 >= 0 && tmp_num1 % 10 <= 9)
                m++;
            tmp_num1 /= 10;
        }
        if(m == i)  //判断输入的数据每一位是否都小于等于进制数
            break;
        else
        {
            m = 0;  //对计数器m重新初始化
            fflush(stdin);  //清空缓存区
            printf("输入有误！请重新输入：\n");
        }
    }
    //将进制转换的四种情况分别表示
    if(before <= 10 && after <= 10)
    {
        num2 = Ten_LessThanTen(after, LessThanTen_Ten(before, num1));
        printf("\n%d进制的%d对应的%d进制数为：%d\n", before, num1, after, num2);
    }
    else if(before > 10 && after <= 10)
    {
        num2 = Ten_LessThanTen(after, MoreThanTen_Ten(before, array_num1));
        printf("\n%d进制的%s对应的%d进制数为：%d\n", before, array_num1, after, num2);
    }
    else if(before <= 10 && after > 10)
    {
        str_num2 = Ten_MoreThanTen(after, LessThanTen_Ten(before, num1));
        printf("\n%d进制的%d对应的%d进制数为：%s\n", before, num1, after, str_num2);
    }
    else if(before > 10 && after > 10)
    {
        str_num2 = Ten_MoreThanTen(after, MoreThanTen_Ten(before, array_num1));
        printf("\n%d进制的%s对应的%d进制数为：%s\n", before, array_num1, after, str_num2);
    }
    system("pause");
    
    return 0;
}