Rustlings Topic: Functions

in Study Log on Rust, Rustlings

Have a look at how functions work to check further information about Rust functions.

You may find solution code for the topic from my repo.

  1. functions1.rs
  2. functions2.rs
  3. functions3.rs
  4. functions4.rs
  5. functions5.rs

functions1.rs

We can’t use a function without declaring it. Declare an empty function with matching function signature.
That is, function with name call_me & takes no argument and returns nothing.

/* file: "exercises/functions/functions1.rs" */
fn call_me() {

}

fn main() {
    call_me();
}

functions2.rs

Rust requires that all parts of a function’s signature have type annotations. Any integer type will do. i32, u32, usize … Choose the one you like.

/* file: "exercises/functions/functions2.rs" */
fn main() {
    call_me(3);
}

fn call_me(num: u32) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
}

functions3.rs

If we look at the function signature of the call_me(num: u32), the function expects to have one argument. Provide one argument when you call the function from the main function.

/* file: "exercises/functions/functions3.rs" */
fn main() {
    call_me(10);
}

fn call_me(num: u32) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
}

functions4.rs

Rust’s syntax for the return type is fn function_name() -> RET_TYPE. We have to provide type annotation after ->.

/* file: "exercises/functions/functions4.rs" */
fn main() {
    let original_price = 51;
    println!("Your sale price is {}", sale_price(original_price));
}

fn sale_price(price: i32) -> i32 {
    if is_even(price) {
        price - 10
    } else {
        price - 3
    }
}

fn is_even(num: i32) -> bool {
    num % 2 == 0
}

functions5.rs

When we want to return something, we can use good-old-fashioned return this; OR to provide a statement without a semicolon(;). Rust will interpret the statement as a return statement if you don’t provide ;.

At the moment, fn square(num: i32) -> i32 does not have return statement. Remove ; from num * num; to make it as a return statement.

/* file: "exercises/functions/functions5.rs" */
fn main() {
    let answer = square(3);
    println!("The answer is {}", answer);
}

fn square(num: i32) -> i32 {
    num * num
}

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