Day 2: Making Decisions

Code isn’t just a list of instructions from top to bottom. Sometimes we need to branch (if this, then that) or loop (do this 10 times).

1. If / Else Statements

The most basic building block of logic.

const hour = 14; // 2 PM

if (hour < 12) {
    console.log("Good Morning!");
} else if (hour < 18) {
    console.log("Good Afternoon!");
} else {
    console.log("Good Evening!");
}

Truthy & Falsy

In JS, values can be evaluated as true or false.

Falsy: false, 0, "" (empty string), null, undefined, NaN.
Truthy: Everything else (including "0", [], {}).

const username = "";

if (username) {
    console.log(`Welcome ${username}`);
} else {
    console.log("Please log in."); // This runs because "" is falsy.
}

2. Switch Statements

Great for checking a single variable against multiple specific values.

const role = "admin";

switch (role) {
    case "admin":
        console.log("Full Access");
        break;
    case "editor":
        console.log("Edit Access");
        break;
    default:
        console.log("Read Only");
}

3. Loops

For Loop

Use when you know exactly how many times you want to repeat something.

for (let i = 0; i < 5; i++) {
    console.log(`Iteration number ${i}`);
}
// Output: 0, 1, 2, 3, 4

While Loop

Use when you want to loop until a condition is met (be careful of infinite loops!).

let count = 0;
while (count < 3) {
    console.log("Still going...");
    count++;
}

Homework for Day 2:

Write a program that checks a variable age.
If age < 13, log “Child”.
If age between 13 and 19, log “Teenager”.
Otherwise, log “Adult”.
Bonus: Use a loop to print all even numbers from 0 to 20.

Tomorrow, we organize our code with Functions!

Day 2: Control Flow & Loops