volatile unsigned char *dirf, *dirk, *dirc, *dira, *dirl, *dirb;
volatile unsigned char *bit4, *bit3, *bit2, *bit1, *key_in, *key_out;

// display on sevenseg using integer as input
void sevenseg(volatile unsigned char *reg ,volatile char dig=10,volatile bool dot=0){
  volatile char dot_add;
  if(dot){
    dot_add=0x80;
  }else
    dot_add=0;
  switch(dig){
    case 0: *reg=0x3f|dot_add; break;  //0
    case 1: *reg=0x06|dot_add; break;  //1
    case 2: *reg=0x5b|dot_add; break;  //2
    case 3: *reg=0x4f|dot_add; break;  //3
    case 4: *reg=0x66|dot_add; break;  //4
    case 5: *reg=0x6d|dot_add; break;  //5
    case 6: *reg=0x7d|dot_add; break;  //6
    case 7: *reg=0x07|dot_add; break;  //7
    case 8: *reg=0x7f|dot_add; break;  //8
    case 9: *reg=0x6f|dot_add; break;  //9
    default: *reg=0x79|dot_add; break;  //E
  }
}

// 7seg with keypad data
void sevenseg_keypad(volatile unsigned char *reg, volatile char i, volatile char j){
  switch(i){
    case 0: {
        switch(j){
          case 0: *reg=0x06; break;  //1
          case 1: *reg=0x5b; break;  //2
          case 2: *reg=0x4f; break;  //3
          default: *reg=0x80; break; // dot
        }break;
    }
    case 1: {
      switch(j){
          case 0: *reg=0x66; break;  //4
          case 1: *reg=0x6d; break;  //5
          case 2: *reg=0x7d; break;  //6
          default: *reg=0x80; break; // dot
      }break;
    }
    case 2: {
      switch(j){
          case 0: *reg=0x07; break;  //7
          case 1: *reg=0x7f; break;  //8
          case 2: *reg=0x6f; break;  //9
          default: *reg=0x80; break; // dot
      }break;
    }
    case 3:{
      switch(j){
        case 1: *reg=0x3f; break;  //0
        default: *reg=0x80; break; // dot
      }break;
    }
    default:
      *reg=0x80; break;
  }
}

// keypad scanning 
volatile unsigned char read_keypad(volatile char i, volatile char j){
  switch(i){
    case 0: {
        switch(j){
          case 0: return 1;  //1
          case 1: return 2;  //2
          case 2: return 3;  //3
          case 3: return '+';  //+
          //default: *reg=0x80; break; // dot
        }break;
    }
    case 1: {
      switch(j){
          case 0: return 4;  //4
          case 1: return 5;  //5
          case 2: return 6;  //6
          case 3: return '-'; //-
          //default: *reg=0x80; break; // dot
      }break;
    }
    case 2: {
      switch(j){
          case 0: return 7;  //7
          case 1: return 8;  //8
          case 2: return 9;  //9
          case 3: return '*';
        //  default: *reg=0x80; break; // dot
      }break;
    }
    case 3:{
      switch(j){
        case 1: return 0;  //0
        case 2: return '=';  //0
        //default: *reg=0x80; break; // dot
      }break;
    }
    //default:
    //  *reg=0x80; break;
  }
}

void add(volatile unsigned long num1,volatile unsigned long num2){
  volatile unsigned long result=0;
  result=num1+num2;
  if(result<10000){
    sevenseg(bit1,result%10);
    result/=10;
    sevenseg(bit2,result%10);
    result/=10;
    sevenseg(bit3,result%10);
    result/=10;
    sevenseg(bit4,result%10);
  }else{
    // display default values EEEE
    sevenseg(bit1);
    sevenseg(bit2);
    sevenseg(bit3);
    sevenseg(bit4);
  }
  
}

void setup() {
  // put your setup code here, to run once:
  dirf=0x30; dirk=0x107; dirc=0x27; dira=0x21; dirl=0x10a; dirb=0x24;
  *dirf=0xff; *dirk=0xff; *dirc=0xff; *dira=0xff; *dirl=0x0f; *dirb=0x00;
  bit4=0x31; bit3=0x108; bit2=0x28; bit1=0x22; key_out=0x10b; key_in=0x23;

  volatile unsigned long inp,dig=0,num1=0, num2=0;
  volatile unsigned char operat=0;

  while(dig<4){
    for(volatile char i=0;i<4;i++){
      *key_out=1<<i;
      for(volatile char j=0;j<4;j++){
        inp=*key_in;
        if((inp&(1<<j))==(1<<j)){
          // stop entering num1 if operator is entered
          if(read_keypad(i,j)=='+'){
            operat=read_keypad(i,j);
            dig=4;
            for(volatile long del=0;del<100000;del++);
            // skip the current iteration
            continue;
          }
          // enter num1
          num1=num1*10+read_keypad(i,j);
          sevenseg(bit1,read_keypad(i,j));
          for(volatile long del=0;del<100000;del++);
          dig++;

          
        }
      }
    }
  }
  
  // enter operator only if num1 is 4 digits, otherwise operator taken from above only
  if(!operat){
    dig=0;
    while(dig<1){
      for(volatile char i=0;i<4;i++){
        *key_out=1<<i;
        for(volatile char j=0;j<4;j++){
          inp=*key_in;
          if((inp&(1<<j))==(1<<j)){
            if(read_keypad(i,j)=='+'){
            operat=read_keypad(i,j);
            dig++;
            for(volatile long del=0;del<100000;del++);
            }
          }
        }
      } 
    }
  }
  dig=0;

  // enter num2
  while(dig<4){
    for(volatile char i=0;i<4;i++){
      *key_out=1<<i;
      for(volatile char j=0;j<4;j++){
        inp=*key_in;
        if((inp&(1<<j))==(1<<j)){
          // stop entering num2 if = is occured 
          if(read_keypad(i,j)=='='){
            dig=4;
            for(volatile long del=0;del<100000;del++);
            continue;
          }
          num2=num2*10+read_keypad(i,j);
          sevenseg(bit1,read_keypad(i,j));
          for(volatile long del=0;del<100000;del++);
          dig++;   
        }
      }
    }
  }

  if(operat=='+'){
    add(num1,num2);
  }
  
}

void loop() {
  // put your main code here, to run repeatedly:
  
}