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Day 3 — Loops & Conditional Statements

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

📌 Topic of the Day

##notes : https://drive.google.com/file/d/1v3HDmEBw5-Mc1zVyB6-mgiBOqnMcBiTG/view?usp=sharing

Loops & Conditional Statements — keeping it light, making it stick

Conditionals decide what to do. Loops decide how many times to do it. Together they power almost every algorithm you'll ever write.

🎥 Resource

Language Resource
☕ Java Loops & Conditionals — Tutorial
🐍 Python Same concepts — find equivalent in CampusX 100 Days of Python
⚙️ C++ Same concepts — Love Babbar / Striver playlist

🧠 What to Learn Today

Conditional Statements

if / else if / else

  • Checks a boolean condition — only ONE branch runs
  • Java/C++: if (condition) {} | Python: if condition:
  • Common mistake: = is assignment, == is comparison

Ternary Operator

  • One-line if-else: int max = (a > b) ? a : b;
  • Python: max_val = a if a > b else b
  • Use for simple conditions only — don't nest ternaries

switch Statement (Java & C++)

  • Cleaner than long if-else chains for exact value matching
  • Always add break — without it, execution falls through to the next case
  • Python has no switch — use if-elif or a dictionary

Loops

for loop — use when you know the count

for (int i = 0; i < 5; i++) { }         // Java / C++
for i in range(5):     # 0–4
for i in range(1, 6):  # 1–5
for i in range(0, 10, 2):  # 0,2,4,6,8

while loop — use when you don't know the count

while (condition) { }   // Java / C++
while condition:        # Python
  • Always ensure the condition eventually becomes false — or you get an infinite loop

do-while — runs body at least once, then checks condition

do { } while (condition);   // Java & C++ only
  • Python has no do-while — simulate with while True: ... if cond: break

break and continue

Keyword What it does
break Immediately exits the loop
continue Skips current iteration, goes to next

Nested Loops

  • A loop inside a loop
  • Two nested loops = O(n²) — be aware of this in DSA

💻 Practice Questions

Solve in Java (or your language). Push solutions to your fork.

1. Area of Circle

Formula: π × r² (use Math.PI in Java)

2. Area of Triangle

Formula: ½ × base × height

3. Area of Rectangle

Formula: length × breadth

4. Area of Isosceles Triangle

Formula: ½ × base × height

5. Area of Parallelogram

Formula: base × height

6. Area of Rhombus

Formula: ½ × d1 × d2 (d1 and d2 are the diagonals)

7. Area of Equilateral Triangle

Formula: (√3 / 4) × side²

8. Perimeter of Circle (Circumference)

Formula: 2 × π × r

9. Perimeter of Equilateral Triangle

Formula: 3 × side

10. Perimeter of Parallelogram

Formula: 2 × (a + b) (a and b are adjacent sides)

💡 For all questions: take input from the user, calculate, and print the result rounded to 2 decimal places.

✅ Checklist Before You Sleep

  • I understand how if / else if / else flows
  • I know the difference between = and ==
  • I can write a ternary operator
  • I know when to use switch vs if-else
  • I know the for loop structure: init ; condition ; update
  • I understand while vs do-while
  • I know what break and continue do
  • Solved at least 6 of the 10 practice questions

💬 Community

Stuck on any formula or syntax? Drop it in the community.

Solved all 10? Drop a 🔥 in the community.

Next up → Day 4: Functions, Methods & Introduction to Recursion