Functions

• Statement - instructions that perform some action and do not return a value.
• Expression - evaluate to a resulting value.

This is a statement:

let x = 5;

This is an expression:

5

Statements do not return values. Therefore, you can’t assign a let statement to another variable.

let x = (let y = 6); //Error

Calling a function is an expression (hello()), calling a macro is an expression (println!("Guess the number!")), and the block used to create new scopes {} is an expression:

{
    let x = 5;
    x - 2
}

The above expression evaluates to 3.

Expressions do not include semi-colons. If you add a semi-colon, it becomes a statement and will not return a value.