Complete Coding Basics Study Guide | Centauri CS Resources

💻 Overview

Programming is the process of giving instructions to a computer to perform specific tasks. These instructions are written in programming languages that the computer can understand. This guide covers the fundamental building blocks that are common across most programming languages.

What You'll Learn

Variables: How to store and manage data
Data Types: Different kinds of data (numbers, text, etc.)
Operators: How to perform calculations and comparisons
Conditionals: Making decisions in your code
Loops: Repeating actions efficiently
Functions: Organizing code into reusable blocks

📦 Variables

A variable is like a labeled box that stores data. You give it a name, and you can put a value inside it. Later, you can retrieve or change that value.

                    
// Creating variables
let playerName = "Alex";      // Stores text
let score = 100;               // Stores a number
let isGameOver = false;       // Stores true/false

// Changing a variable's value
score = 150;                   // Now score is 150
                    
                

Variable Naming Rules

Must start with a letter, underscore (_), or dollar sign ($)
Can contain letters, numbers, underscores, dollar signs
Cannot use reserved keywords (like if, for, while)
Are case-sensitive (score ≠ Score)

💡 Best Practice: Use Descriptive Names

Use playerScore instead of ps or x. Clear names make your code easier to understand.

📊 Data Types

Data types tell the computer what kind of data a variable holds. Different types behave differently.

Type	Description	Example
String	Text (letters, words, sentences)	`"Hello, World!"`
Number/Integer	Whole numbers	`42`, `-7`, `0`
Float/Double	Decimal numbers	`3.14`, `-0.5`
Boolean	True or false values	`true`, `false`
Array/List	Collection of values	`[1, 2, 3, 4]`

                    
// Different data types
let name = "Sarah";           // String
let age = 25;                  // Number (Integer)
let height = 5.7;              // Float
let isStudent = true;         // Boolean
let colors = ["red", "blue", "green"];  // Array
                    
                

🔢 Operators

Arithmetic Operators

Operator	Name	Example	Result
`+`	Addition	`5 + 3`	8
`-`	Subtraction	`10 - 4`	6
`*`	Multiplication	`6 * 7`	42
`/`	Division	`20 / 4`	5
`%`	Modulus (remainder)	`17 % 5`	2

Comparison Operators

Operator	Meaning	Example	Result
`==`	Equal to	`5 == 5`	true
`!=`	Not equal to	`5 != 3`	true
`>`	Greater than	`10 > 5`	true
`<`	Less than	`3 < 8`	true
`>=`	Greater than or equal	`5 >= 5`	true
`<=`	Less than or equal	`4 <= 7`	true

Logical Operators

Operator	Name	Description
`&&`	AND	Both conditions must be true
`\|\|`	OR	At least one condition must be true
`!`	NOT	Reverses the boolean value

🔀 Conditionals (If/Else)

Conditionals let your program make decisions based on whether something is true or false.

                    
let age = 18;

if (age >= 18) {
    console.log("You can vote!");
} else {
    console.log("You're too young to vote.");
}
                    
                

📖 Multiple Conditions (else if)

                        
let score = 85;

if (score >= 90) {
    console.log("Grade: A");
} else if (score >= 80) {
    console.log("Grade: B");
} else if (score >= 70) {
    console.log("Grade: C");
} else {
    console.log("Grade: F");
}
// Output: Grade: B
                        
                    

🧠 Remember the Flow

IF this → THEN that → ELSE something else

🔄 Loops

Loops let you repeat code multiple times without writing it over and over.

For Loop

Use when you know how many times to repeat.

                    
// Print numbers 1 to 5
for (let i = 1; i <= 5; i++) {
    console.log(i);
}
// Output: 1, 2, 3, 4, 5
                    
                

For Loop Breakdown

let i = 1 → Start at 1 (initialization)
i <= 5 → Keep going while i is ≤ 5 (condition)
i++ → Add 1 to i each time (increment)

While Loop

Use when you don't know how many times to repeat.

                    
let count = 0;

while (count < 3) {
    console.log("Count is: " + count);
    count++;
}
// Output: Count is: 0, Count is: 1, Count is: 2
                    
                

⚠️ Infinite Loop Warning

Always make sure your loop has a way to stop! If the condition never becomes false, your program will freeze.

⚙️ Functions

Functions are reusable blocks of code that perform a specific task. Think of them as mini-programs within your program.

                    
// Defining a function
function greet(name) {
    return "Hello, " + name + "!";
}

// Calling the function
let message = greet("Alex");
console.log(message);  // Output: Hello, Alex!
                    
                

Function Parts

Name: What you call the function (greet)
Parameters: Inputs the function accepts (name)
Body: The code inside the curly braces
Return: The value the function gives back

📖 Function Example: Calculate Area

                        
function calculateArea(width, height) {
    return width * height;
}

let area = calculateArea(5, 10);
console.log(area);  // Output: 50

💡 Why Use Functions?

Reusability: Write once, use many times
Organization: Break complex problems into smaller parts
Readability: Give meaningful names to blocks of code
Debugging: Easier to find and fix errors

✏️ Practice Problems

Problem 1 Easy

What will be printed? let x = 10; x = x + 5; console.log(x);

Answer: 15

Explanation: x starts at 10. Then we add 5 to it (10 + 5 = 15) and store it back in x.

Problem 2 Medium

Write a function that takes a number and returns "even" or "odd".

                            
function checkEvenOdd(num) {
    if (num % 2 === 0) {
        return "even";
    } else {
        return "odd";
    }
}

console.log(checkEvenOdd(4));  // "even"
console.log(checkEvenOdd(7));  // "odd"
                            
                        

The modulus operator (%) gives the remainder. If a number divided by 2 has remainder 0, it's even.

Problem 3 Medium

Write a loop that prints the numbers 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 (countdown).

                            
for (let i = 10; i >= 1; i--) {
    console.log(i);
}

// Alternative with while loop:
let count = 10;
while (count >= 1) {
    console.log(count);
    count--;
}
                            
                        

Note: i-- decreases i by 1 each iteration (opposite of i++).

Problem 4 Hard

Write a function that calculates the factorial of a number. (Example: 5! = 5 × 4 × 3 × 2 × 1 = 120)

                            
function factorial(n) {
    let result = 1;
    for (let i = n; i >= 1; i--) {
        result = result * i;
    }
    return result;
}

console.log(factorial(5));  // 120
console.log(factorial(3));  // 6
                            
                        