Master conditional logic by building a grade calculator that maps numeric scores to letter grades. Sharpen your programming skills today!

Conditionals

[00:00] Great. Let's do this. So we're gonna start by creating a variable called grade. So we're gonna make that a let because we're gonna change it. We'll set it explicitly to a string.

[00:11] Because we're not setting it to anything, now TypeScript doesn't know what this is so it gives it what's called an any type, which is basically just anything, and it's not very helpful from a types perspective. So we're gonna specifically say this is a string. We're not gonna assign it to anything though, so it is not it doesn't actually have a value until we've assigned it to something. And now, we've got our score right here. We're going to say if the score is greater than or equal to 90, and we hopefully you remember some of these comparators that we did, these comparisons right here, then, yeah, then it's an a.

[00:49] Otherwise, b, c, d. Or if it's anything lower than 60, then, yeah, you're gonna get an f. My I I was gonna say my apologies, but, like, I didn't do anything wrong. It was your grade, man. So I do better next time.

[01:07] Alright. And, then we're going to make a past. I'm not going to assign this to Boolean. I'm gonna try to ease you into learning about inference and things. So we're not actually going to assign this a specific type because it's able to infer that based off of the logic that we've got or the expression that we have on the right side of that equal sign.

[01:30] So if the grade is not a d and it's not an f, then we know that we passed and we can console log all of that. Whoops. Console log. There we go. And we can export, save that, and here we go.

[01:41] Score was an 85. That's a b. We passed. Hooray. If you want to, as just some extra credit, you could go through here and do b plus and b minus and and, all of that.

[01:52] So feel free to to play around with that. But, yeah. This is the, the the basics of using if and else. This is our, comparison right here. This is what determines whether we're going to fall into, this if this if block right here.

[02:12] This is called the consequent. So what happens in the case that this expression evaluates to true? And then, you can have an else if. So you can have an if all by itself and that's it. And if we do that, then we're gonna get our grade is undefined because we're not handling, the case of less than 90.

[02:31] You can do actually, we could redo this whole thing without, whoops. There we go. Without these else, right here. And ultimately, that would, end up being, yeah, that would not end up being the same because we're saying, hey, if the score is greater than or equal to 60, then give me a d. And so what's happening here is we're saying if the score is greater than or equal to 90, that's an a.

[02:56] Ours is not, so we're gonna pass through that. Then if it's greater than or equal to 80, then the grade is a b and then, as a totally separate statement, if it's greater than 70, that's a c. Okay. Well, now it gets changed to c. And then as there's another totally separate statement, if it's greater than or equal to 60, then that's a d.

[03:14] So that else part of the the the clause there, that, special syntax, that keyword is actually important for, tying those if and else statements together. So if this, then basically the what the else is saying oops. Else. The else right here is saying, if it's not that but it's this, then continue. But if we leave that off, then we're just saying, if it's this and, yeah, of course, it it's, greater than 80, it's also greater than 70 and so that's where we end up in that situation.

[03:49] You could rewrite this a little bit to make, this format work without the else statements. So you could say, if score is, oh, yeah. Here we go. Is greater than or equal to 80 and the score is less than 90, then that would work. And we do that all on the all of these.

[04:06] Then, we're going to get the same result here. But between you and me, I think let's just use the else if statements because I think, it's a lot easier to understand how all of that works. So, you wanna think about how the code flows. So you basically, you put a value for the, relevant variables in your mind and you kinda follow the code flow and that will make things a little bit more straightforward. Alright.

[04:32] I think that's everything that you need to know there. So I hope you enjoyed that one and we'll see you in the next one.

[00:00] So for this exercise, we are going to make a grade calculator using conditional logic. We're going to say, if your grade number is this, then that's an a, etcetera, etcetera. So, I'm gonna let you just jump into this one and we'll see you when you're done.

Learning to program can feel overwhelming. There are countless tutorials, boot camps, and YouTube videos all pulling you in different directions, and most of them assume you already know something.

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## Expressions & Output

Every program needs a way to tell you what it's doing. Without output, you're flying blind-- writing code with no way to verify it works. This is the very first skill you need as a developer.

In this section, you'll get your programs talking back to you while learning the building blocks of every piece of code you'll ever write:

- Outputting values with `console.log`
- String expressions and concatenation
- Number expressions and arithmetic operators
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## Variables

Hardcoded values can only get you so far. Real programs need to store, reference, and update data as they run. Without a solid understanding of how variables work, you'll constantly be confused by unexpected behavior.

Variables are foundational to every program you'll ever write. Here you'll learn how to declare them, when to use each type, and a critical nuance that trips up even experienced developers:

- Declaring variables with `let` and `const`
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- Reassigning values with `let` and compound operators like `+=`
- The important distinction between reassignment and mutation
- Why `const` doesn't always mean the value can't change

## Primitive Types

JavaScript has types whether you think about them or not. Every value in every variable carries a type, and ignoring that fact leads to bugs that are hard to track down. TypeScript makes these types explicit, catching entire categories of errors before your code ever runs.

This section introduces you to all seven primitive types and how TypeScript helps you work with them safely:

- Explicit type annotations with `number`, `string`, and `boolean`
- The difference between `null` and `undefined`
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## Comparisons & Boolean Logic

Making decisions is at the heart of every program. Should this button be enabled? Does this user have access? Is the cart empty? All of these questions boil down to comparisons and boolean logic.

Getting comparisons wrong leads to subtle bugs that are painful to debug. This section gives you the tools to write conditions that behave exactly as you'd expect:

- Loose equality (`==`) vs. strict equality (`===`) and why you should almost always use strict
- Not-equal, greater-than, and less-than-or-equal-to operators
- Combining conditions with logical AND (`&&`), OR (`||`), and NOT (`!`)
- Order of operations with logical operators
- Using parentheses to make complex conditions explicit

## Truthiness & Falsiness

JavaScript has a unique feature where every value has an inherent "truthiness" or "falsiness." This isn't a bug-- it's one of the most practical features of the language once you understand it. But misunderstanding it leads to some of the most confusing behavior new developers encounter.

Here you'll learn which values are truthy, which are falsy, and how to use this knowledge to write cleaner conditional logic:

- Coercing values to booleans with the `Boolean` constructor
- The double-not (`!!`) operator and when to use it
- Falsy values: `0`, `""`, `null`, `undefined`, `false`, and `NaN`
- Practical patterns like checking array length and optional values
- Avoiding common pitfalls with logical operators and coercion

## Functions

Up to this point, your programs run top to bottom and that's it. Functions change everything. They let you take a chunk of code, put it somewhere reusable, and call it from anywhere-- with different inputs each time.

Functions are the single most important building block for organizing and scaling your programs. This section takes you from writing your first function through passing functions as arguments to other functions:

- Function declarations with the `function` keyword
- Accepting parameters and specifying their types
- Return values and TypeScript's return type inference
- Arrow functions and implicit returns
- Passing functions as arguments to other functions
- Documenting your functions with JSDoc

## Type Inference & Arrow Functions

TypeScript is smart. You don't have to type everything explicitly-- TypeScript can often figure out the types for you by looking at your code. Knowing when to lean on inference and when to be explicit is a skill that makes your code cleaner and your development faster.

This section also covers arrow functions, a concise alternative syntax you'll see everywhere in modern JavaScript and TypeScript:

- How TypeScript infers return types from your function body
- When explicit return types help catch bugs earlier
- Converting function declarations to arrow functions
- Implicit returns for single-expression functions
- The hoisting difference between declarations and expressions
- Function expressions as first-class values

## Void & Never

Not every function returns something useful, and some code paths should never be reached. TypeScript has dedicated types for both of these situations, and understanding them helps you write more precise, self-documenting code.

This section introduces two TypeScript-specific concepts that complete your understanding of the type system's fundamentals:

- The `void` type for functions that don't return a value
- How `void` relates to `undefined` in practice
- The `never` type for functions that throw errors or never return
- Using `never` to enforce exhaustive checks
- Throwing errors to halt execution and signal failures
- Practical patterns for input validation with error throwing

Programming Foundations

Structured Data

Type Safety

Object Oriented TypeScript

Advanced TypeScript

Practical TypeScript: Foundations to Fluency

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Conditionals

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