Functions

Functions in Rust

Functions are declared with fn, followed by the name, parameters, and an optional return type:

fn add(x: i32, y: i32) -> i32 {
    x + y
}

Expressions vs Statements

Rust is an expression-based language. The last expression in a function body is implicitly returned — no return keyword needed:

fn double(x: i32) -> i32 {
    x * 2  // no semicolon — this is the return value
}

Adding a semicolon turns an expression into a statement (which returns ()):

fn oops(x: i32) -> i32 {
    x * 2; // ERROR: expected i32, found ()
}

Early Return

Use return to return early:

fn first_positive(v: &[i32]) -> Option<i32> {
    for &x in v {
        if x > 0 {
            return Some(x); // early return
        }
    }
    None // implicit return at the end
}

Recursion

Functions can call themselves:

fn factorial(n: u64) -> u64 {
    if n <= 1 { 1 } else { n * factorial(n - 1) }
}

Your Task

Implement three functions:

1. max_of_three(a: i32, b: i32, c: i32) -> i32 — returns the largest of three integers.
2. factorial(n: u64) -> u64 — returns n! (factorial). Note: 0! = 1.
3. is_prime(n: u32) -> bool — returns true if n is a prime number.