let firstNum = undefined
let secondNum = undefined
let operator = undefined

function add(x, y) {
    return Number(x + y);
}

function subtract(x, y) {
    return x - y;
}

function multiply(x, y) {
    return x * y;
}

function divive(x, y) {
    if (x === 0) {
        return 0
    } else if (y === 0) {
        alert("Cannot divide by 0!");
    }
    return x / y;
}

function operate(firstNum, secondNum, operator) {
    switch (operator) {
        case '+':
            return add(firstNum, secondNum);
        case '-':
            return subtract(firstNum, secondNum);
        case '*':
            return multiply(firstNum, secondNum);
        case '/':
            return divive(firstNum, secondNum);
    }
}