Intro to Rust. | ECOSYSTEM Research

Rust 101: Basic Syntax Cheat Sheet A quick reference for the core building blocks of Rust. --- 1. Variables Type annotations (optional — Rust infers types) Common integer types | Type | Size | Range (approx.) | |---|---|---| | i8 / u8 | 8-bit | −128…127 / 0…255 | | i32 / u32 | 32-bit | ±2.1 billion / 0…4.2 billion | | i64 / u64 | 64-bit | very large | | usize | pointer-sized | used for indexing | i = signed (can be negative), u = unsigned (only ≥ 0). Constants --- 2. Functions Key rule: The last expression without a semicolon is the return value. Adding ; turns it into a statement that returns (). --- 3. Math Operators Shortcuts Useful methods Type casting ⚠️ Integers and floats cannot be mixed directly. 1 + 2.0 is an error — cast first. --- 4. Logic & Comparison Comparison operators (return bool) Boolean operators Short-circuit evaluation: false && anything never evaluates the right side. --- 5. Control Flow if / else if / else if as an expression Both branches must return the same type. match (like a switch, but better) loop (infinite until break) while for (most common — iterate over a range or collection) Loop labels (for nested loops) --- 6. Collections (quick peek) Arrays — fixed size, same type Vectors — growable Tuples — mixed types, fixed size --- 7. Strings Use {} in println! to format any printable value. Use {:?} for debug output (e.g., arrays, vectors, tuples). --- 8. Comments --- 9. Common Beginner Mistakes | Mistake | Fix | |---|---| | Forgetting mut | Add mut: let mut x = 5; | | Mixing int and float | Cast: x as f64 | | Missing return semicolon rule | Remove ; on the last line to return a value | | Assigning to an immutable var | Declare with mut | | Using = instead of == in a condition | Comparisons use == | | Forgetting & when passing a string literal | fn f(s: &str) not fn f(s: String) | --- 10. Small Practice Program Put it all together: Rust 101: Simple Greeting Program Here's a beginner-friendly program that covers the essentials: printing, variables, and reading user input. How to run it 1. Save the file as main.rs 2. In your terminal, run: Or, if you're using Cargo: What's happening (line by line) | Piece | What it does | |---|---| | use std::io; | Brings in Rust's input/output module so we can read from the keyboard. | | fn main() | Every Rust program starts here. | | println!(...) | Prints text to the console (the ! means it's a macro). | | let mut name = String::new(); | Creates a mutable variable holding an empty string. mut is required because we'll modify it. | | io::stdin().readline(&mut name) | Reads a line of text from the user and stores it in name. The &mut passes a mutable reference. | | .expect(...) | Handles errors — if reading fails, the program crashes with this message. | | name.trim() | Removes the newline \n that readline leaves behind. |