void setup() {
  volatile char *dirf,*dirk,*dira,*dirc;  
  
  dirf = 0x30;  dirk = 0x107; dira = 0x21; dirc = 0x27;
 *dirf = 0x0f; *dirk = 0x00; *dira = 0xff; *dirc = 0x0f;
}
void loop(){
  display_add();
}
void display_add(){
  volatile char *outf,*outa,*outc,*ink,x;
  volatile int i,num ,count,sum,tl,cs,add;
  outf = 0x31;ink = 0x106; outc = 0x28;outa = 0x22; 
  volatile char numbers[]={0xC0,0xF9,0xA4,0xB0,0X99,0X92,0X82,0xF8,0x80,0x90};
  sum = 0;
  add = 0;
  tl = 0;
  cs = 0;
  while(1){
    for(i=0;i<4;i++){
      *outf=1 << i;
      x=*ink;
      if(x!=0){//checks if any switch is pressed on keypad
        if(*outf==1 && x == 1){//row 1 column 1 (1)
          num = 1;
        }
        if(*outf==1 && x == 2){//row 1 column 2 (2)
          num = 2;
        }
        if(*outf==1 && x == 4){//row 1 column 3 (3)
          num = 3;
        }
        if(*outf==2 && x == 1){// row 2 column 1 (4)
          num = 4;
        }
        if(*outf==2 && x == 2){// row 2 column 2 (5)
          num = 5;
        }
        if(*outf==2 && x == 4){// row 2 column 3 (6)
          num = 6;
        }
        if(*outf==4 && x == 1){// row 3 column 1 (7)
          num = 7;
        }
        if(*outf==4 && x == 2){// row 3 column 2 (8)
          num = 8;
        }
        if(*outf==4 && x == 4){// row 3 column 3 (9)
          num = 9;
        }
        if(*outf==8 && x == 2){// row 4 column 2 (0)
          num = 0;
        }
        tl = (tl*10)+num;
        //display pressed number
        *outc=0x01;
        *outa=numbers[num];
        delay(200);
        
        //add button
        if(*outf == 1 && x == 8){
          cs = tl;
          add++;
        }
        // function of = button
        if(*outf == 8 && x == 4 && add>0){
          int ld,vl;
          ld = tl%10;
          vl = (cs/10)+ld;
          int tens,ones;
          tens = vl/10;
          ones = vl%10;
          *outc = 0x01;
          *outa = numbers[tens];
          delay(500);
          *outc = 0x02;
          *outa = numbers[ones];
          delay(500);
          tl = 0;
          add = 0;
        }
         
      }
    }  
  }
}