#define ret_ok  0
#define ret_err 1

char week_day[8] = {"Monday","Tuesday","Wedsday","Thursday","Friday","Saturday","Sunday"};

int Judge_day_of_the_week(int week_num,char *result_week_day)
{   
    if( week_num < 1 || week_num > 7 )
    {
        printf("Your input is error\n");
        return ret_err;
    }
    else
    {
        *result_week_day = week_day[week_num-1];
    }

    return ret_ok;
}