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.
Creating a Function
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
}Calling a Function
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 functionFunctions with Parameters
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.
Functions with Return Values
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.
Why Use Functions?
- To organize your code
- To avoid repeating the same code
- To make your programs easier to read and change