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FREE INTERACTIVE NOTES · C & C++ WEEK 1 OF 8

Hello, C! The Language of Machines ⚙️

Python talks to computers. C practically IS the computer. Rockets, robots and game engines run on what you learn this week.

1Meet your team

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Chip the Gear: Welcome to C! I'm Chip. C is older, stricter and FASTER than Python — it's the language operating systems and robots are built with. Respect it, and it gives you superpowers.
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Bittu: In Python I interpret line by line. In C, your whole program is compiled into machine code FIRST — then I run it at maximum speed. 🏎️
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Professor Hoot: Don't worry about installing anything today — onlinegdb.com runs C in your browser. In class we set up GCC properly.
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Bugly: And I'm still here! C gives you more power… which means MORE ways to meet me. Hehehe.

2Your first C program

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Chip: Every C program has this skeleton: #include brings in tools, main() is where execution starts, every statement ends with a ; and return 0 says "all went well".
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Bugly: Forget ONE semicolon and the compiler refuses to build anything. In Python I let you run and THEN crash. C stops you at the door. 😤

3Variables — with name tags for types

In C you must announce the TYPE of every box: int for whole numbers, float for decimals, char for single letters.

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Professor Hoot: printf uses placeholders: %d for int, %f for float, %c for char, %s for text. The values fill the blanks in order.

4The integer division surprise 😲

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Chip: int ÷ int = int — the decimal is THROWN AWAY. Python's / would say 3.5; C says 3. Make one number a float (7.0) to keep the decimals.

Division Machine — C style!

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7 / 2 = 3 (int!)  ·  7 % 2 = 1  ·  7.0 / 2 = 3.5

5scanf — reading input

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Bugly: See that & before age? Forget it and… well, you'll meet me in Week 4. It means "the ADDRESS of age" — scanf needs to know WHERE to put the answer.

6Decisions — if / else, C edition

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Chip: Same logic as Python's Day 4 — but C uses { curly braces } instead of indentation, and conditions wear (brackets).

7Quick quiz! 🧠

In C, what is 9 / 2?
💡 int ÷ int = int. The .5 is thrown away — 4. (For 4.5, write 9.0 / 2.)
What happens if you forget a semicolon in C?
💡 C checks EVERYTHING before running. No semicolon, no program. Strict but fair.

8Your mission 🚀

Mission 1: On onlinegdb.com, print your name and your dream company in two printf lines.
Mission 2: Make int marks = 87 and print "I scored 87!" using %d.
Mission 3: Delete a semicolon on purpose, read the compiler's complaint, fix it. First blood against Bugly!

Week 1 complete — you speak machine now! ⚙️

Next week: loops, functions and recursion — C picks up speed.

Go to Week 2: Loops & Functions →

⚔️ Or test yourself in the C & C++ Arcade →