Module 1Variables & TypesLesson 5 of 1024 min

Scalar Types Deep Dive

Integers, floats, bools, chars — choosing types for prices, sizes, and flags.

Integer families

Type	Range idea	Quant use
`i32`	default signed	days, small counts
`i64`	large signed	order ids, timestamps (ms)
`u32`/`u64`	unsigned	sizes that can't be negative
`isize`/`usize`	pointer-sized	indices, lengths

Underscores help readability: 1_000_000.

Floats

f64 — default; use for most math (rates, vols, spots)
f32 — half size, less precision; rarely first choice for risk

Important: binary floats are not decimal money. For display/rounding you manage precision; for true decimal cash some shops use integer cents or decimal crates later.

Bool and char

rust

let is_open = true;
let grade = 'A'; // Unicode scalar — single quotes

Overflow behavior

Debug: overflow often panics
Release: wraps for primitives
Prefer checked_add, saturating_add when sizes matter

rust

fn main() {
    let q: u32 = 10;
    println!("{:?}", q.checked_add(20)); // Some(30)
}

Output

Some(30)

Example: simple interest

rust

fn simple_interest(p: f64, r: f64, t: f64) -> f64 {
    p * r * t
}

Exercise

Compute simple interest and future value; print with clear labels.

Challenge

Use checked_add on two u32 day counts (180 + 90) and print the Option.

Tips

Prefer f64 for market math unless you have a fixed-point standard
Cast with 'as' carefully — prefer same types in expressions
u32 for quantities if negatives are invalid

Try it live

Scalar Types Deep DiveRust 2021

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Output

Press Run to compile and execute.