Kashish Dugar

Rebuilding the guessing game from memory

I had 20 minutes to rebuild my guessing game with the book closed. I remembered the secret number from 1 to 100, the loop, too low and too high, “You win!” and break. Then I opened the book and made a list of everything I couldn’t remember.

What each part means

• let and let mut: let is like my lane number, it stays the same the whole race. let mut is like my lap count, it can change. The secret number uses let, my guess uses let mut.
• String::new(): an empty glass, ready before you pour the smoothie.
• read_line: pouring the guess into the glass.
• .expect(): what Rust says if the glass cracks while pouring.
• Ok and Err: like a parcel. Ok means it arrived. Err means it came back. If I type a word instead of a number, Err happens and continue asks me to guess again.
• parse: turns my guess into a number, because a string can’t be too high or too low.
• match: picks one of three answers: too low, too high or you win.
• loop and break: like swimming laps until the coach blows the whistle. “You win!” and break are the whistle.

My errors

• My Cargo.toml said rand = 0.1.8. Rust said “invalid float”. It needed quote marks and the right version: "0.8.5".
• I used >= instead of => in match.
• I forgot println! on the Too high line. Rust said the match arms have incompatible types.

My prediction page

From today I write my prediction on paper before every run.

Rust Chapter 3.1: Variables and Mutability

• mut means we can change the value. Plain let means we can’t.
• Shadowing: you write let again to make a new variable with the same name.
• Constants are written in ALL CAPS and can never be mut.

I also started a Python vs Rust table: print is println! and while is like loop.

Petzold: Bit by Bit by Bit

I always write the place values from the right first. 1100 = 12 and 10101 = 21.

A bit is one yes-or-no answer: a 0 or a 1. To guess which of 4 smoothie flavours someone picked, you only need 2 yes-or-no questions. 2 bits give 4 messages, and everyone must agree on the code. A whistle means nothing unless me and my coach agreed on what it is.