问在c#中使用getch()只接受数字和字母作为输入

EN

char c;
int temp = 0;
while((c= getch()) !='\r')
{
    if ((temp == -32) || (temp == 0))
    {
    }
    else
    {
        if(isalnum((char)c) == 0)
        {
            if((c == '\'') || (c == -118) || (c == -115) || (c == -107) || (c == -123) || (c == -105))
            {
                printf("true: %c\n",c);
            }
            else
                printf("false: %d\n",c);
        }
        else
        {
            printf("true: %c\n",c);
        }
    }
    temp = c;
}