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Functions

A function is a block of code that only runs when you call it.

Functions are used to organize your code, avoid repeating yourself, and make your program easier to understand.

To create a function, use the fn keyword, followed by the function name and a set of parentheses () and curly braces {} :

Example

fn
function_name
() {
 // code to be executed
}

Now that you have created a function, you can execute it by calling it.

To call a function, write the name of the function followed by two parantheses () .

Example

// Create a function
fn say_hello() {
  println!("Hello from a function!");
}
say_hello();
// Call the function

You can send information into a function using parameters. Parameters are written inside the parentheses () .

Example

fn greet(name: &str) {
  println!("Hello, {}!", name);
}
greet("John");

In this example, the function takes a string parameter called name and prints it in the greeting message.

A function can also return a value.

Use the -> symbol in the function header to show what type of value will be returned.

Inside the function, use the return keyword to send the value back:

Example

fn add(a: i32, b: i32) -> i32 {
  return a + b;
}
let sum = add(3, 4);
println!("Sum is: {}", sum);

This function adds two numbers and returns the result.

In Rust, you can omit the return keyword. Just write the value on the last line of the function, without a semicolon :

Example

fn add(a: i32, b: i32) -> i32 {
  a + b
}
let sum = add(3, 4);
println!("Sum is: {}", sum);

The last line a + b is automatically returned.

Both examples do the same thing. It is up to you which one to use.