关于网页中十六进制解码问题

#include<stdio.h>
//%D6  %D0  %B9  %FA  4个字节 8  32
//%D6   //1101  13   0110  6   =13*16+6
//%D0   //1101  13  0000  0    13*16

//-55
// 10    11    12     13
//‘A‘ 65  B 66 C  67  D 68
void main1()
{
    char strx[7] = "%D6%D0";
    char str[3] = { 0 };
    //str[0]= 214;//‘D‘ ‘6‘  13*16+6
    //str[1]=208;//‘D‘ ‘0‘   13*16+0

    str[0] = (‘D‘ - 55) * 16 + ‘6‘ - 48;
    str[1] = (‘D‘ - 55) * 16 + ‘0‘ - 48;
    printf("%s", str);

    getchar();
}

char* change(char *str)
{
    char *tempstr = malloc(strlen(str) + 1);//strlen
    //memset(tempstr, 0, sizeof(str) + 1);
    int x=0, y=0;
    char assii_1, assii_2;
    while (tempstr[x])
    {
        if ((tempstr[x]=str[y]) ==‘%‘)
        {
            //y+1 y+2
            if (str[y+1]>=‘A‘)
            {
                assii_1 = str[y + 1] - 55;

            }
            else
            {
                assii_1 = str[y + 1] - 48;
            }
            if (str[y + 2] >= ‘A‘)
            {
                assii_2= str[y + 2] - 55;
            }
            else
            {
                assii_2 = str[y + 2] - 48;
            }
            tempstr[x] = assii_1 * 16 + assii_2;

            y += 2;

        }
        x++;
        y++;
    }
    tempstr[x] = ‘\0‘;

    return tempstr;

}

void main()
{
    char str[128] = "%D6%DC%C8%F0%B8%A3";
    printf("%s", change(str));

    system("pause");

}