Floats and casts

Rust has two floating-point types: f32 and f64. Prefer f64, which is the default for literals like 2.5. Floats and integers never mix implicitly: 3 + 0.5 is a compile error. Convert explicitly with as:

let n: i32 = 7;
let half = n as f64 / 2.0;   // 3.5
let whole = 3.99_f64 as i32; // 3

Rules worth remembering:

• Float to integer truncates toward zero: -2.7 as i32 is -2. Values out of range saturate at the integer's limits.
• Integer to a narrower integer keeps only the low bits: 300 as u8 is 44.
• as binds tighter than /, so n as f64 / 2.0 casts n first.

For rounding, floats have methods: .round(), .floor(), .ceil() and .abs(). To round to two decimals, scale up, round, and scale back down:

let x = 3.14159_f64;
let r = (x * 100.0).round() / 100.0; // 3.14

Because floats are approximate, tests compare them with a small tolerance rather than exact equality.

Your task

Write these public functions:

• average(a: i32, b: i32) -> f64: the exact mean, so average(1, 2) is 1.5.
• truncate(x: f64) -> i32: drop the fractional part with as.
• round_to_cents(x: f64) -> f64: round to two decimal places.