Rust For Loop

What is a For Loop in Rust?

A for loop in Rust is used to iterate over a sequence of items. It eliminates the need for manual index handling, making the loop cleaner, safer and less error-prone.

Syntax of the For Loop

for variable in iterable {
    // Code to execute
}

• variable: Represents each item in the sequence.
• iterable: A collection, range, or any iterator over which the loop iterates.

Advantages of Using the For Loop in Rust

1. Safety: No need for manual index management, reducing the risk of runtime errors.
2. Efficiency: Rust optimizes iteration to be fast and memory-safe.
3. Clarity: Code becomes easier to read and maintain.

Examples of For Loop in Rust

1. Iterating Over a Range

You can use a for loop to iterate over a range of numbers.

fn main() {
    for number in 1..5 {
        println!("Number: {}", number);
    }
}

Output:

Number: 1  
Number: 2  
Number: 3  
Number: 4  

• The range 1. .5 includes numbers from 1 to 4, but excludes 5.
• To include the upper bound, use 1. .=5.

2. Iterating Over an Array

The for loop can iterate through an array or a vector.

fn main() {
    let fruits = ["apple", "banana", "cherry"];

    for fruit in fruits {
        println!("Fruit: {}", fruit);
    }
}

Output:

Fruit: apple  
Fruit: banana  
Fruit: cherry  

3. Iterating Over a Vector

Vectors are commonly used in Rust. The for loop easily iterates over them.

fn main() {
    let numbers = vec![10, 20, 30, 40];

    for num in &numbers {
        println!("Number: {}", num);
    }
}

Output:

Number: 10  
Number: 20  
Number: 30  
Number: 40  

• Using &numbers allows the loop to borrow the vector without taking ownership.

4. Iterating with Indices

The .enumerate() method provides both the index and the value during iteration.

fn main() {
    let colors = ["red", "green", "blue"];

    for (index, color) in colors.iter().enumerate() {
        println!("Index: {}, Color: {}", index, color);
    }
}

Output:

Index: 0, Color: red  
Index: 1, Color: green  
Index: 2, Color: blue  

Working with Ranges in For Loops

a. Exclusive Range (. .)

Iterates up to, but not including, the upper bound.

rustCopy codefor i in 1..5 {
    println!("{}", i);
}

b. Inclusive Range (. .=)

Iterates up to and includes the upper bound.

for i in 1..=5 {
    println!("{}", i);
}

Using Break and Continue in For Loops

Break Statement

Exits the loop prematurely.

fn main() {
    for i in 1..10 {
        if i == 5 {
            break;
        }
        println!("{}", i);
    }
}

Output:

1  
2  
3  
4  

Continue Statement

Skips the current iteration and proceeds to the next one.

fn main() {
    for i in 1..10 {
        if i == 5 {
            continue;
        }
        println!("{}", i);
    }
}

Output:

1  
2  
3  
4  
6  
7  
8  
9  

Nested For Loops

You can use for loops inside other loops to handle multi-dimensional data or complex tasks.

Example: Multiplication Table

fn main() {
    for i in 1..=3 {
        for j in 1..=3 {
            print!("{} ", i * j);
        }
        println!();
    }
}

Output:

1 2 3  
2 4 6  
3 6 9  

Iterating Over Strings

You can iterate over characters in a string.

fn main() {
    let word = "Rust";

    for c in word.chars() {
        println!("{}", c);
    }
}

Output:

R  
u  
s  
t