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JavaScript

Web & Node.js

Arrays, async/await, DOM manipulation, fetch API, and modern ES6+ features.

Array Filter

const nums = [1, 2, 3, 4, 5];
const even = nums.filter(n => n % 2 === 0);
// [2, 4]

Array Map

const nums = [1, 2, 3];
const doubled = nums.map(n => n * 2);
// [2, 4, 6]

Array Reduce

const nums = [1, 2, 3, 4];
const sum = nums.reduce((a, b) => a + b, 0);
// 10

Fetch API

const res = await fetch('/api/data');
const data = await res.json();
console.log(data);

Destructuring

const { name, age } = user;
const [first, ...rest] = items;

Spread Operator

const merged = [...arr1, ...arr2];
const copy = { ...obj, newKey: val };

Async/Await

async function getData() {
  try {
    const res = await fetch(url);
    return await res.json();
  } catch (e) { console.error(e); }
}

Promise.all

const results = await Promise.all([
  fetch('/api/1'),
  fetch('/api/2')
]);

Python

General Purpose

Lists, dictionaries, file operations, list comprehensions, and data processing.

List Comprehension

squares = [x**2 for x in range(10)]
evens = [x for x in nums if x % 2 == 0]

Dict Comprehension

squared = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

Read File

with open('file.txt', 'r') as f:
    content = f.read()
    lines = f.readlines()

Write File

with open('file.txt', 'w') as f:
    f.write('Hello World')

Dictionary

user = {'name': 'John', 'age': 30}
name = user.get('name', 'Unknown')
user['email'] = '[email protected]'

Lambda Function

double = lambda x: x * 2
sorted_list = sorted(items, key=lambda x: x['name'])

Try/Except

try:
    result = risky_operation()
except Exception as e:
    print(f"Error: {e}")

String Format

name = "World"
msg = f"Hello, {name}!"
formatted = "{:.2f}".format(3.14159)

PHP

Web Development

Arrays, string functions, file handling, and web development patterns.

Array Map

$nums = [1, 2, 3, 4, 5];
$squared = array_map(fn($n) => $n * $n, $nums);
// [1, 4, 9, 16, 25]

Array Filter

$nums = [1, 2, 3, 4, 5];
$evens = array_filter($nums, fn($n) => $n % 2 === 0);
// [2, 4]

Array Reduce

$nums = [1, 2, 3, 4];
$sum = array_reduce($nums, fn($a, $b) => $a + $b, 0);
// 10

JSON Encode/Decode

$json = json_encode($data);
$arr = json_decode($json, true);

String Functions

$lower = strtolower($str);
$parts = explode(',', $csv);
$joined = implode('-', $arr);

File Operations

$content = file_get_contents('file.txt');
file_put_contents('out.txt', $data);

Null Coalescing

$name = $_GET['name'] ?? 'Guest';
$value = $arr['key'] ?? $default;

Array Sort

sort($arr);  // ascending
rsort($arr); // descending
usort($arr, fn($a, $b) => $a - $b);

Go

Systems & Backend

Slices, goroutines, HTTP servers, error handling, and concurrent programming.

HTTP GET

resp, err := http.Get(url)
if err != nil { return err }
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)

Goroutine

go func() {
    // concurrent work
    result <- processData()
}()

Slice Operations

nums := []int{1, 2, 3}
nums = append(nums, 4, 5)
slice := nums[1:3] // [2, 3]

Map Operations

m := make(map[string]int)
m["key"] = 42
val, ok := m["key"]

Error Handling

result, err := doSomething()
if err != nil {
    return fmt.Errorf("failed: %w", err)
}

JSON Marshal

data, _ := json.Marshal(obj)
json.Unmarshal(data, &result)

Channel

ch := make(chan int, 10)
ch <- 42  // send
val := <-ch  // receive

Defer

file, _ := os.Open("file.txt")
defer file.Close()
// file auto-closes when func returns

Java

Enterprise & Android

Collections, streams, lambda expressions, and object-oriented patterns.

Stream Filter

List<Integer> evens = nums.stream()
    .filter(n -> n % 2 == 0)
    .collect(Collectors.toList());

Stream Map

List<String> names = users.stream()
    .map(User::getName)
    .collect(Collectors.toList());

Lambda Expression

list.forEach(item -> {
    System.out.println(item);
});
list.sort((a, b) -> a.compareTo(b));

Optional

Optional<String> opt = Optional.ofNullable(val);
String result = opt.orElse("default");
opt.ifPresent(v -> process(v));

HashMap

Map<String, Integer> map = new HashMap<>();
map.put("key", 42);
int val = map.getOrDefault("key", 0);

Try-with-resources

try (var reader = new FileReader("f.txt")) {
    // auto-closes
} catch (IOException e) {
    e.printStackTrace();
}

String Operations

String[] parts = str.split(",");
String joined = String.join("-", list);
boolean contains = str.contains("test");

Stream Reduce

int sum = nums.stream()
    .reduce(0, Integer::sum);
// or .reduce(0, (a, b) -> a + b)

Ruby

Web & Scripting

Blocks, iterators, hashes, and elegant object-oriented programming.

Array Select

evens = nums.select { |n| n.even? }
odds = nums.reject { |n| n.even? }

Array Map

squares = nums.map { |n| n ** 2 }
names = users.map(&:name)

Hash Operations

user = { name: 'John', age: 30 }
name = user[:name] || 'Unknown'
user.merge!(email: '[email protected]')

Block Iterator

5.times { |i| puts i }
(1..10).each { |n| puts n }
arr.each_with_index { |v, i| }

String Interpolation

name = "World"
msg = "Hello, #{name}!"
multi = <<~TEXT
  Multiple lines
TEXT

Reduce/Inject

sum = nums.reduce(0) { |acc, n| acc + n }
# or simply: nums.sum

C++

C / C++

Systems Programming

Vectors, pointers, memory management, and standard template library.

Vector Operations

vector<int> nums = {1, 2, 3};
nums.push_back(4);
nums.pop_back();
int size = nums.size();

Range-based For

for (const auto& item : items) {
    cout << item << endl;
}

Smart Pointer

auto ptr = make_unique<MyClass>();
auto shared = make_shared<MyClass>();
ptr->doSomething();

Lambda Expression

auto add = [](int a, int b) { return a + b; };
sort(v.begin(), v.end(), [](int a, int b) {
    return a < b;
});

Map/Unordered Map

unordered_map<string, int> m;
m["key"] = 42;
if (m.find("key") != m.end()) { }

String Operations

string s = "hello";
s += " world";
size_t pos = s.find("world");
string sub = s.substr(0, 5);

SQL

Databases

Queries, joins, aggregations, subqueries, and database manipulation.

SELECT with JOIN

SELECT u.name, o.total
FROM users u
JOIN orders o ON u.id = o.user_id
WHERE o.total > 100;

GROUP BY

SELECT category, COUNT(*) as count,
       SUM(price) as total
FROM products
GROUP BY category;

INSERT

INSERT INTO users (name, email)
VALUES ('John', '[email protected]');

INSERT INTO users (name) VALUES
('A'), ('B'), ('C');

UPDATE

UPDATE users
SET email = '[email protected]',
    updated_at = NOW()
WHERE id = 1;

Subquery

SELECT * FROM users
WHERE id IN (
  SELECT user_id FROM orders
  WHERE total > 1000
);

CASE Statement

SELECT name,
  CASE
    WHEN score >= 90 THEN 'A'
    WHEN score >= 80 THEN 'B'
    ELSE 'C'
  END as grade
FROM students;

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