For Loops in Rust

Hello! In this lesson, we're going to dive into for loops in Rust — a fundamental control structure used to iterate over sequences. For loops allow you to iterate over a range of numbers, items in a collection, or even characters in a string. Mastering for loops is critical for writing efficient and readable code. Let's dive in!

A for loop in Rust iterates over a range or a collection. The basic syntax looks like this:

fn main() {
    for var in range {
        code to execute
    }
}

• The for keyword starts the loop.
• The in keyword specifies the range or collection to iterate over.
• The code block inside {} runs for each item in the specified range.

Let's take a look at an example:

fn main() {
    // For loop with range
    for number in 1..6 {
        println!("Number is: {}", number);
    }
}
/* Output
    Number is: 1
    Number is: 2
    Number is: 3
    Number is: 4
    Number is: 5
*/

The syntax 1..6 is a range expression in Rust that represents a sequence of numbers starting from 1 up to, but not including, 6. It uses the .. operator to create this range. So, 1..6 generates the sequence: 1, 2, 3, 4, 5.

In each iteration of the loop, the variable number takes on the specified value in the range.

Rust provides a convenient way to iterate in reverse using the rev method. The range includes the integers 1 up to, but not including, 6. Since the last element of the range is 5, the for loop starts at 5 and continues down to 1.

fn main() {
    for number in (1..6).rev() {
        println!("Reverse number is: {}", number);
    }
}
/* Output
    Reverse number is: 5
    Reverse number is: 4
    Reverse number is: 3
    Reverse number is: 2
    Reverse number is: 1
*/

In this example:

• The rev method is called on the range 1..6.
• This makes the loop iterate from 5 down to 1.

Sometimes, you may need to iterate with a custom step size. The step_by method allows you to specify the step size. step_by takes an integer argument that specifies the number of steps to jump.

fn main() {
    // Using step_by to iterate
    for number in (1..8).step_by(2) {
        println!("{}", number); 
    }
}
/* Output
    1
    3
    5
    7
*/

In this example, the loop iterates over the range 1..8 with a step size of 2.