console.log('my' + ' cat');
console.log('1' + 2);
console.log(`string literals: 1 + 2 = ${1 + 2}`);

console.log(1 + 1); // add
console.log(1 - 1); // substract
console.log(1 / 1); // divide
console.log(1 * 1); // multiply
console.log(5 % 2); // remainder
console.log(2 ** 3); // exponentiation

let counter = 2;
const preIncrement = ++counter;
// counter = counter + 1;
// preIncrement = counter;
console.log(`preIncrement: ${preIncrement}, counter: ${counter}`);
const postIncrement = counter++;
// postIncrement = counter;
// counter = counter + 1;
console.log(`postIncrement: ${postIncrement}, counter: ${counter}`);
const preDecrement = --counter;
console.log(`preDecrement: ${preDecrement}, counter: ${counter}`);
const postDecrement = counter--;
console.log(`postDecrement: ${postDecrement}, counter: ${counter}`);

let x = 3;
let y = 6;
x += y; // x = x + y;
x -= y;
x *= y;
x /= y;

console.log(10 < 6); // less than
console.log(10 <= 6); // less than or equal
console.log(10 > 6); // greater than
console.log(10 >= 6); // greater than or equal

const ellie1 = { name: 'ellie' };
const ellie2 = { name: 'ellie' }; //ellie1과 ellie2는 서로 다른 레퍼런스를 가리킨다.
const ellie3 = ellie1;
console.log(ellie1 == ellie2); //reference값이 다르므로 false
console.log(ellie1 === ellie2); //reference값이 다르므로 false
console.log(ellie1 === ellie3); //reference값을 ellie1에 할당한 것이라 true

// equality - puzzler
console.log(0 == false); //값이 다르므로 true
console.log(0 === false); //타입이 다르므로 false
console.log('' == false); //true
console.log('' === false); //타입이 다르므로 false
console.log(null == undefined); //true
console.log(null === undefined); //타입이 다르므로 false

### 13. for loop (for 반복문)
```css
//for loop, for(begin; condition; step)
for (i = 3; i > 0; i--) {
  console.log(`for: ${i}`);
}

for (let i = 3; i > 0; i = i - 2) {
  // inline variable declaration
  console.log(`inline variable for: ${i}`);
}

for (let i = 0; i < 10; i++) {
  for (let j = 0; j < 10; j++) {
    console.log(`i: ${i}, j:${j}`);
  }
}