👋 Hi there, coding explorer!

Welcome back! This week, we’re diving into Loops and Functions — from beginner concepts to expert-level techniques perfect for coding interviews and real projects. We’ll break everything into small, easy-to-digest bites, so you can practice and master them step by step.

Part 1: Functions

1️⃣ What is a Function?

A function is a reusable block of code that performs a specific task. Think of it as a recipe: you provide ingredients (inputs), it performs steps (code), and gives a finished dish (output).

2️⃣ Function Terminology

Function Name

  • Identifies the function so you can call it later.

def greet():  # "greet" is the function name
    print("Hello!")

function greet() {
  console.log("Hello!");
}

Parameters

  • Placeholders for inputs the function expects.

def greet(name):  # "name" is a parameter
    print(f"Hello, {name}!")

function greet(name) {
  console.log(`Hello, ${name}!`);
}

Arguments

  • Actual values passed to the function.

greet("Fahim")  # "Fahim" is the argument

greet("Fahim");

Return Value

  • The output a function gives back.

def add(a, b):
    return a + b
print(add(5,3))  # 8

function add(a,b){ return a+b; }
console.log(add(5,3)); // 8

Function Keyword

  • Python: def

  • JavaScript: function or arrow functions

const greet = (name) => `Hello, ${name}!`;

Default Parameters

def greet(name="Guest"):
    print(f"Hello, {name}!")
greet()        # Hello, Guest
greet("Fahim") # Hello, Fahim

function greet(name="Guest"){ console.log(`Hello, ${name}!`); }
greet(); greet("Fahim");

Anonymous Functions

  • Python: lambda

  • JavaScript: arrow functions

square = lambda x: x*x
print(square(5))  # 25

const square = x => x*x;
console.log(square(5)); // 25

Higher-Order Functions

  • Functions that take other functions or return functions

def apply_func(func, value):
    return func(value)
print(apply_func(lambda x:x*2, 5))  # 10

function applyFunc(func, value){ return func(value); }
console.log(applyFunc(x=>x*2,5)); // 10

Recursion

  • Function calling itself (common in interviews)

def factorial(n):
    if n==0: return 1
    return n*factorial(n-1)
print(factorial(5))  # 120

function factorial(n){
    if(n===0) return 1;
    return n*factorial(n-1);
}
console.log(factorial(5)); // 120

Concepts:

  • Closures (functions “remembering” scope)

  • Decorators / Wrappers (modifying function behavior)

  • Generators / Iterators (lazy sequences)

  • Memoization / DP prep (optimizing recursion)

3️⃣ Built-in Functions

Python: len(), sum(), sorted(), zip(), map(), filter(), reduce()
JavaScript: parseInt(), Math.max(), Array.isArray(), map(), filter(), reduce()

nums = [1,2,3,4]
print(list(map(lambda x:x*2,nums)))   # [2,4,6,8]
print(list(filter(lambda x:x%2==0,nums)))  # [2,4]

let nums=[1,2,3,4];
console.log(nums.map(x=>x*2));       // [2,4,6,8]
console.log(nums.filter(x=>x%2===0)); // [2,4]

4️⃣ Mini Function Challenge

  1. Write introduce(name, age) → "Hi, I'm Fahim and I am 30 years old."

  2. Add a default parameter for age = 25

  3. Try lambda / arrow function version

Part 2: Loops

1️⃣ What is a Loop?

Loops let you repeat code multiple times until a condition is met. Think of it as running a conveyor belt: the same action happens for every item until all are processed.

2️⃣ Loop Types

Loop Type

Description

Example

for loop

Repeat a block a fixed number of times

for i in range(5): print(i)

while loop

Repeat until a condition is false

while x<5: x+=1

for..of / for..in

Iterate over arrays or object keys (JS)

for(let val of arr)

3️⃣ Loop Keywords

Break – exit the loop early
Continue – skip to the next iteration
Nested Loops – loops inside loops

for i in range(3):
    for j in range(2):
        print(i,j)

for(let i=0;i<3;i++){
    for(let j=0;j<2;j++){
        console.log(i,j);
    }
}

4️⃣ Loop Patterns

  • Two Pointers / Sliding Window – fsequence problems

  • Loop Optimization – minimize iterations

  • Loop Invariants – maintain correct logic in each iteration

  • Nested Loops for Matrix / Grid problems

5️⃣ Mini Loop Challenge

  1. Print all numbers from 1 to 20.

  2. Print even numbers only.

  3. Nested loop: print all pairs from [1,2,3] and [a,b].

  4. Expert: Find the maximum sum of 3 consecutive numbers in an array using a loop.

6️⃣ AI Tip 🤖

Ask AI:
"Write a function that uses a loop to sum all even numbers in an array and return the result."

This combines functions + loops, which is a classic interview problem.

✅ Sign-off

That’s your Loops & Functions Bite — Beginner to Expert! 🎉

Experiment with nested loops, break/continue, sliding windows, and combine with functions to solve real interview-style problems.

Next time, we’ll dive into Arrays, building on what you’ve learned today.

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