script.js

const currentEl = document.getElementById('current');
const previousEl = document.getElementById('previous');
const keys = document.querySelector('.keys');

let current = '0';
let previous = '';
let operator = null;
let resetNext = false;

function updateDisplay() {
  currentEl.textContent = current;
  if (operator) {
    const opMap = { '+': '+', '-': '−', '*': '×', '/': '÷' };
    previousEl.textContent = `${previous} ${opMap[operator] || operator}`;
  } else {
    previousEl.textContent = '';
  }
}

function inputNumber(num) {
  if (resetNext) { current = ''; resetNext = false; }
  if (num === '.' && current.includes('.')) return;
  if (current === '0' && num !== '.') { current = num; }
  else { current += num; }
  updateDisplay();
}

function chooseOperator(op) {
  if (current === '' && previous === '') return;
  if (previous !== '' && operator && !resetNext) { compute(); }
  operator = op;
  previous = current;
  resetNext = true;
  updateDisplay();
}

function compute() {
  if (previous === '' || operator === null) return;
  const a = parseFloat(previous);
  const b = parseFloat(current);
  let result;
  switch (operator) {
    case '+': result = a + b; break;
    case '-': result = a - b; break;
    case '*': result = a * b; break;
    case '/': result = b === 0 ? 'Error' : a / b; break;
    default: return;
  }
  current = String(Math.round(result * 1e10) / 1e10);
  operator = null;
  previous = '';
  resetNext = true;
  updateDisplay();
}

function clearAll() {
  current = '0'; previous = ''; operator = null; resetNext = false;
  updateDisplay();
}

function deleteLast() {
  if (resetNext) return;
  if (current.length > 1) { current = current.slice(0, -1); }
  else { current = '0'; }
  updateDisplay();
}

function percent() {
  current = String(parseFloat(current) / 100);
  updateDisplay();
}

keys.addEventListener('click', (e) => {
  const key = e.target.closest('.key');
  if (!key) return;
  if (key.dataset.number !== undefined) inputNumber(key.dataset.number);
  else if (key.dataset.operator) chooseOperator(key.dataset.operator);
  else if (key.dataset.action === 'equals') compute();
  else if (key.dataset.action === 'clear') clearAll();
  else if (key.dataset.action === 'delete') deleteLast();
  else if (key.dataset.action === 'percent') percent();
});

document.addEventListener('keydown', (e) => {
  if (e.key >= '0' && e.key <= '9') inputNumber(e.key);
  else if (e.key === '.') inputNumber('.');
  else if (['+', '-', '*', '/'].includes(e.key)) chooseOperator(e.key);
  else if (e.key === 'Enter' || e.key === '=') { e.preventDefault(); compute(); }
  else if (e.key === 'Backspace') deleteLast();
  else if (e.key === 'Escape') clearAll();
});

updateDisplay();