Conditionals and Loops

Control flow in Rust revolves around two main constructs: conditional expressions to decide which execution path to take, and loop constructs to repeat instructions.

Conditionals: if as an Expression

In Rust, the if statement is an expression, meaning it returns a value. We can use if to directly assign a value to a variable:

let condition = true;
let number = if condition { 5 } else { 6 }; // if/else as an expression

Loops and Iterations

Rust provides three types of native loops: loop, while, and for.

1. loop (Infinite Loop)

The loop keyword creates an infinite loop that continues until you explicitly tell it to stop using break:

let mut count = 0;
loop {
    count += 1;
    if count == 10 {
        break; // Exit the loop
    }
}

Additionally, you can return a value from a loop by placing it right after break:

let result = loop {
    count += 1;
    if count == 10 {
        break count * 2; // Returns 20
    }
};

2. while (Conditional Loop)

Runs a block of code as long as a boolean condition remains true:

let mut number = 3;
while number != 0 {
    println!("{}!", number);
    number -= 1;
}

3. for (Iteration over Collections and Ranges)

The for loop is the most common and safest tool for iterating over elements in a collection or a range of numbers:

// Iterates over numbers 1 through 3 (excluding 4)
for number in 1..4 {
    println!("Valore: {}", number);
}

// Iterates including the right boundary using '='
for number in 1..=3 {
    println!("Valore: {}", number); // Prints 1, 2 and 3
}

Loop Labels

When dealing with nested loops, break and continue statements apply to the innermost loop by default. Rust allows you to use a loop label (written as 'label_name:) to explicitly terminate or continue an outer loop:

let mut count = 0;
'outer: loop {
    loop {
        if count == 5 {
            break 'outer; // Exits the outer loop directly
        }
        count += 1;
    }
}

Try it yourself