How can I use mktime for displaying weekday ?

uint32_t THH,TMM,TSS,WEEKDAY,DATE,MONTH,YEAR;
 unsigned char date[20],day[30],month[20],year[20],hour[20],min[20],sec[32];
 char *weekday_label[]={"Sun","Mon","Tue","Wed","Thr","Fri","Sat"};
 char *month_label[]={"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sept","Oct","Nov","Dec"};
  struct tm *utcTimeSnapshot = NULL;
  time_t Tmp;
 /* Load the Counter value */
 Tmp = RTC_GetCounter();

 utcTimeSnapshot = localtime(&Tmp);
 /* Compute day */
// WEEKDAY = ((Tmp / 86400)%7)+1;
WEEKDAY = utcTimeSnapshot->tm_wday;


 /* Compute date */
 //DATE = ((Tmp / 31556926)%365)-40;
 // DATE = ((Tmp / 86400)%365)-41;
DATE = utcTimeSnapshot->tm_mday;

/* Compute month */
 //MONTH = ((Tmp / 2629743)%12);
MONTH = (utcTimeSnapshot->tm_mon)-1;

 

 /* Compute year */
//YEAR = (Tmp / 31556926)+1970;
YEAR = (utcTimeSnapshot->tm_year)+1900;


 /* Compute hours */
// THH = ( Tmp / 3600 ) % 24;
THH = utcTimeSnapshot->tm_hour;

 /* Compute minutes */
 //TMM = ( Tmp / 60 ) % 60;
TMM = utcTimeSnapshot->tm_min;

 /* Compute seconds */
 //TSS = Tmp % 60;
TSS = utcTimeSnapshot->tm_sec;
mktime(utcTimeSnapshot);
        // printf("GET TIME");
      //lcd_cmd(LCD_CLEAR);
      sprintf(day,"%.2d",WEEKDAY);
      sprintf(date,"%.2d",DATE);
      //sprintf(month,"%02d",MONTH);
      sprintf(year,"%.2d",YEAR);
      sprintf(hour,"%.2d",THH);  //convert integer to string
      sprintf(min,"%.2d",TMM);  //convert integer to string
      sprintf(sec,"%.2d",TSS);  //convert integer to string
      //lcd_string("HOUR:MIN:SEC");
      lcd_xy(0,0);

      if (utcTimeSnapshot && (utcTimeSnapshot->tm_wday >= 0) && (utcTimeSnapshot->tm_wday <= 6))
        {
          lcd_string(weekday_label[utcTimeSnapshot->tm_wday]);lcd_string(",");
           printf ("That day is a %s.\n", weekday_label[utcTimeSnapshot->tm_wday]);

        }
        else
          lcd_string("???,");
      //lcd_string(weekday_label[WEEKDAY]);lcd_string(",");
      //lcd_string(day);
      lcd_string(date);lcd_string("-");
      lcd_string(month_label[MONTH]);
      //lcd_string(month);
      lcd_string("-");lcd_string(year);
      lcd_xy(1,0);
      
      
      lcd_cmd(SECOND_ROW);
      lcd_string(hour);lcd_string(":");
      lcd_string(min);lcd_string(":");
      lcd_string(sec);
     

}