function calc() {
var num1 = Number(document.querySelector('#num1').value);
var num2 = Number(document.querySelector('#num2').value);
var select = document.querySelector('select');
var operator = select.options[select.selectedIndex].value; var result;
if (operator == 'sum') {
result = num1 + num2;
} else if (operator == 'sub') {
result = num1 - num2;
}else if (operator == 'multiply'){
result = num1 * num2;
}else if (operator == 'div'){
result = num1/num2;
} else { result = 'Invalid operator'; }
result1.innerHTML = result ;
}