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Day 5 — Functions & Methods

DSA Partner Challenge | Week 1: Language Basics + Maths for DSA

📌 Topic of the Day

##notes : https://drive.google.com/file/d/1mBk6GyKOxVWvhnH_aF5sHUXRIDBPxFZv/view?usp=sharing Functions & Methods — write once, use anywhere

Every DSA algorithm you'll write will live inside a function. Today we learn how to define them, call them, pass data in, and get data out — across all 3 languages.

🎥 Resource

Language Resource
☕ Java Functions & Methods Tutorial
🐍 Python Same concepts — CampusX 100 Days of Python (Functions section)
⚙️ C++ Same video — Love Babbar / Striver playlist

🧠 What to Learn Today

Why Functions?

  • Write code once → reuse it anywhere
  • Keeps programs organised and readable
  • Easier to test, debug, and fix
  • In DSA: every algorithm = a function

Java — Methods

// Syntax
public static returnType methodName(parameters) {
    // body
    return value;  // omit if void
}

void method — does something, returns nothing:

public static void greet(String name) {
    System.out.println("Hello, " + name);
}
greet("Tripti");   // Hello, Tripti

Return type method:

public static int add(int a, int b) {
    return a + b;
}
int result = add(5, 3);   // 8

Method Overloading — same name, different parameters:

public static int add(int a, int b)       { return a + b; }
public static double add(double a, double b) { return a + b; }
public static int add(int a, int b, int c)   { return a+b+c; }

Pass by Value — Java copies primitives:

void doubleIt(int x) { x = x * 2; }   // only changes copy
int num = 5;
doubleIt(num);
System.out.println(num);   // still 5!

Python — Functions

def function_name(parameters):
    # body
    return value   # optional

Basic example:

def add(a, b):
    return a + b

result = add(5, 3)   # 8

Return multiple values (Python exclusive):

def min_max(a, b, c):
    return min(a,b,c), max(a,b,c)

low, high = min_max(3, 1, 7)   # low=1, high=7

Default parameters:

def greet(name, msg="Hello"):
    print(f"{msg}, {name}!")

greet("Tripti")          # Hello, Tripti!
greet("Tripti", "Hi")    # Hi, Tripti!

*Variable arguments (args):

def total(*numbers):
    return sum(numbers)

total(1, 2, 3, 4, 5)   # 15

C++ — Functions

returnType functionName(parameters) {
    // body
    return value;
}

Pass by Reference (C++ exclusive with &):

// Pass by value — original unchanged
void doubleIt(int x)  { x = x * 2; }

// Pass by reference — original IS changed
void doubleIt(int& x) { x = x * 2; }

int num = 5;
doubleIt(num);
cout << num;   // 10 if &, 5 without

Default parameters:

void greet(string name, string msg = "Hello") {
    cout << msg << ", " << name;
}
greet("Tripti");           // Hello, Tripti
greet("Tripti", "Hi");     // Hi, Tripti

Forward Declaration (if function is defined after main):

int add(int a, int b);   // declare first

int main() {
    cout << add(2, 3);
}

int add(int a, int b) { return a + b; }   // define later

Quick Comparison

Feature Java Python C++
Define public static int f() def f(): int f()
Return nothing void None (implicit) void
Default params No (use overloading) Yes Yes
Multiple returns No Yes No
Overloading Yes No Yes
Pass by reference No (objects by ref) No Yes (&)
Must be in class Yes No No

💻 Practice Questions

Solve in your language. Define proper methods/functions — don't write everything in main().

1. Find if a number is palindrome or not

A palindrome reads the same forwards and backwards → 121, 1331

2. HCF and LCM of two numbers

HCF: largest number that divides both LCM: smallest number divisible by both → LCM = (a × b) / HCF

3. Vowel or Consonant

Given a character, check if it's a vowel (a,e,i,o,u) or consonant

4. Perfect Number

A number is perfect if sum of its proper divisors = itself → 6 (1+2+3=6)

5. Check Leap Year

Divisible by 4 AND (not divisible by 100 OR divisible by 400)

6. Sum of Digits of a Number

1234 → 1+2+3+4 = 10

7. Kunal's Even Days (August)

Kunal can go out only on even days. Count how many even days are in August (31 days).

8. Sum of negative numbers, sum of positive even numbers, and sum of positive odd numbers from a list

9. Define two methods to print the maximum and minimum among three numbers entered by the user

10. Define a method to find whether a given number is even or odd

11. Voting Eligibility

A person can vote if age >= 18. Define a method that returns true/false.

12. Write a method that takes two numbers as input and returns their sum

13. Sum of N numbers entered by the user — list terminates when user enters 0

✅ Checklist Before You Sleep

  • I can define a function/method in all 3 languages
  • I understand void vs return-type functions
  • I know what parameters and arguments are
  • I understand pass by value vs pass by reference
  • I know what method overloading is (Java / C++)
  • I understand local vs global scope
  • Solved at least 8 of the 13 practice questions

💬 Community

Drop your solutions or any doubts in the community.

Solved all 13? Drop a 🔥 in the community.

Next up → Day 6: Maths for DSA — Part 1 (Prime Numbers, GCD, LCM, Modulo)