First programs based on C programming language📌

Title: What I learned writing my first 4 C programs as a complete beginner 🧠
Intro: 👋 I'm a first-year CSE student and these are the lessons from month 1.
🐛 Why %f prints 140.000000
❓ Why scanf needs the &
⚠️ How 9*c/5 can go wrong with integers
🔗 The code is pasted as text blocks, so you can copy and run it