int ChangeNum(char* str, int length)
{
char  revstr[16] = { 0 };  //根據十六進位制字串的長度，這裡注意陣列不要越界  
int   num[16] = { 0 };
int   count = 1;
int   result = 0;
int tmp = 0;
strcpy(revstr, str);


for (int i = length - 1; i >= 0; i--)
{
if ((revstr[i] >= '0') && (revstr[i] <= '9'))
//num[i] = revstr[i] - 48;//字元0的ASCII值為48 
tmp = revstr[i] - 48;//字元0的ASCII值為48 
else if ((revstr[i] >= 'a') && (revstr[i] <= 'f'))
//num[i] = revstr[i] - 'a' + 10;
tmp = revstr[i] - 'a' + 10;
else if ((revstr[i] >= 'A') && (revstr[i] <= 'F'))
//num[i] = revstr[i] - 'A' + 10;
tmp = revstr[i] - 'A' + 10;
else
//num[i] = 0;
tmp = 0;
//result = result + num[i] * count;
result = result + tmp * count;
count = count * 16;//十六進位制(如果是八進位制就在這裡乘以8)      
}
return result;
}