#define delay_time 500
#include <Wire.h>
#include <LiquidCrystal_I2C.h>


volatile char keypad_num[4][8] = {
    {'1', '2', '0', '3', '0', '0', '0', '+'},
    {'4', '5', '0', '6', '0', '0', '0', '-'},
    {'7', '8', '0', '9', '0', '0', '0', '*'},
    {'C', '0', '0', '=', '0', '0', '0', '/'}
};

LiquidCrystal_I2C lcd(0x27, 16, 2);

void keypad_input_calculation();
void calculation(char *str);


void setup() {
   volatile unsigned char *dirf, *dirk, *outf, *ink ;
    dirk = (volatile char *)0x107; *dirk = 0x00;
    dirf = (volatile char *)0x30; *dirf = 0xff;
    lcd.init();
    lcd.backlight();
}

void loop() {
  keypad_input_calculation();
  delay(delay_time);
}

void keypad_input_calculation() {
    volatile unsigned char *dirf, *dirk, *outf, *ink;
    dirk = (volatile unsigned char *)0x107; *dirk = 0x00;
    dirf = (volatile unsigned char *)0x30; *dirf = 0xff;
    outf = (volatile unsigned char *)0x31;
    ink = (volatile unsigned char *)0x106;
    int j = 0;
    int  k =0;
    char buffer[16] = {0};
  
    while (1) {
        for (volatile long i = 0; i < 4; i++) {
            *outf = 1 << i;
            volatile unsigned char y = *ink;
            if (y != 0) {
                if (i == 3 && y == 1) {//clear the calculator
                    lcd.clear();
                    j = 0;
                    memset(buffer, '\0', sizeof(buffer)); // Clear the buffer
                }
                 else if (i == 3 && y == 4) {//= krne k liye
                    lcd.setCursor(0, 1);
                    calculation(buffer);
                }
                else{//to take input and print on the display
                  buffer[j]= keypad_num[i][y-1];
                  buffer[j+1]='\0';
                  j++;
                  delay(delay_time);
                  while(buffer[k]!='\0'){//priting the string
                  lcd.setCursor(0,0);
                  lcd.print(buffer);
                  k++;
                }
                }
                
            }
        }
    }
}


void calculation(char *str) {
    char t_str1[16] = {0}, t_str2[16] = {0};
    char temp_opr;
    long num1, num2;
    float ans;
    unsigned char i = 0, j = 0;

    // Extract the first number and operator
    while (str[i] != '+' && str[i] != '*' && str[i] != '-' && str[i] != '/' && str[i] != '\0') {
        t_str1[i] = str[i];
        i++;
    }
    t_str1[i] = '\0';
      num1 = atol(t_str1);

    // Extract the operator
    temp_opr = str[i];
    i++;
     memset(t_str1,'\0',16);
    // Extract the second number
    while (str[i] != '\0') {
        t_str1[j] = str[i];
        i++;
        j++;
    }
    t_str1[j] = '\0';

    // Convert extracted strings to numbers
  
    num2 = atol(t_str1);

    // Perform the calculation based on the operator
    switch (temp_opr) {
        case '+':
           
             lcd.setCursor(0, 1);
             lcd.print(num1+num2);
            break;
        case '-':
      
             lcd.setCursor(0, 1);
    lcd.print(num1-num2);
            break;
        case '*':
           
             lcd.setCursor(0, 1);
    lcd.print(num1*num2);
            break;
        case '/':
             lcd.setCursor(0, 1);
    lcd.print((float)num1/num2);
            break;
        default:
            ans = 0;
            break;
    }

    // Print the result on the LCD
   
}