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Rust Practices with Rustlings - Primitive types

Chapter 4 - Primitive types

Exercise 1

fn main() {
    // Booleans (`bool`)

    let is_morning = true;
    if is_morning {
        println!("Good morning!");
    }

    let is_evening; // Finish the rest of this line like the example! Or make it be false!
    if is_evening {
        println!("Good evening!");
    }
}

The first exercise is quite simple, we just need to assign the value to the variable is_evening to make the if statement work.

fn main() {
    // Booleans (`bool`)

    let is_morning = true;
    if is_morning {
        println!("Good morning!");
    }

    let is_evening = true; // or false
    if is_evening {
        println!("Good evening!");
    }
}

Exercise 2

fn main() {
    // Characters (`char`)

    // Note the _single_ quotes, these are different from the double quotes
    // you've been seeing around.
    let my_first_initial = 'C';
    if my_first_initial.is_alphabetic() {
        println!("Alphabetical!");
    } else if my_first_initial.is_numeric() {
        println!("Numerical!");
    } else {
        println!("Neither alphabetic nor numeric!");
    }

    let // Finish this line like the example! What's your favorite character?
    // Try a letter, try a number, try a special character, try a character
    // from a different language than your own, try an emoji!
    if your_character.is_alphabetic() {
        println!("Alphabetical!");
    } else if your_character.is_numeric() {
        println!("Numerical!");
    } else {
        println!("Neither alphabetic nor numeric!");
    }
}

Following the note above

Note the single quotes, these are different from the double quotes

Let's try with the double quote first.

fn main() {
    // Characters (`char`)

    // Note the _single_ quotes, these are different from the double quotes
    // you've been seeing around.
    let my_first_initial = 'C';
    if my_first_initial.is_alphabetic() {
        println!("Alphabetical!");
    } else if my_first_initial.is_numeric() {
        println!("Numerical!");
    } else {
        println!("Neither alphabetic nor numeric!");
    }

    let your_character = "0";// Finish this line like the example! What's your favorite character?
    // Try a letter, try a number, try a special character, try a character
    // from a different language than your own, try an emoji!
    if your_character.is_alphabetic() {
        println!("Alphabetical!");
    } else if your_character.is_numeric() {
        println!("Numerical!");
    } else {
        println!("Neither alphabetic nor numeric!");
    }
}
// Result: Error message - method not found in `&str`

If you use single quote like let your_character = '0'; the exercise will pass.
The reason is because the single quote is for the character type, the double quote is for the string &str.

Exercise 3

fn main() {
    let;

    if a.len() >= 100 {
        println!("Wow, that's a big array!");
    } else {
        println!("Meh, I eat arrays like that for breakfast.");
        panic!("Array not big enough, more elements needed")
    }
}

We need to create an array with more than 100 elements.
Simple, right? We can create an array like this: let a = [1, 2, 3] so type 100 times and we're done! Just kidding, we have another way to do it

fn main() {
    let a = [3; 100];

    if a.len() >= 100 {
        println!("Wow, that's a big array!");
    } else {
        println!("Meh, I eat arrays like that for breakfast.");
        panic!("Array not big enough, more elements needed")
    }
}

FYI: String also has len() method, so you can do this:

fn main() {
    let a = "a".repeat(100);

    if a.len() >= 100 {
        println!("Wow, that's a big array!");
    } else {
        println!("Meh, I eat arrays like that for breakfast.");
        panic!("Array not big enough, more elements needed")
    }
}

Exercise 4

#[test]
fn slice_out_of_array() {
    let a = [1, 2, 3, 4, 5];

    let nice_slice = ;

    assert_eq!([2, 3, 4], nice_slice)
}

A string slice is a reference to part of a String. So we can do this:

fn slice_out_of_array() {
    let a = [1, 2, 3, 4, 5];

    let nice_slice = &a[1..4];

    assert_eq!([2, 3, 4], nice_slice)
}

If you don't pass the reference, example ``a[1..4], the compiler will complain doesn't have a size known at compile-time`.

Exercise 5

fn main() {
    let cat = ("Furry McFurson", 3.5);
    let /* your pattern here */ = cat;

    println!("{} is {} years old.", name, age);
}

cat is a tuple, so we can do this:

fn main() {
    let cat = ("Furry McFurson", 3.5);
    let (name, age) = cat;

    println!("{} is {} years old.", name, age);
}

Exercise 6

fn indexing_tuple() {
    let numbers = (1, 2, 3);
    // Replace below ??? with the tuple indexing syntax.
    let second =;

    assert_eq!(2, second,
        "This is not the 2nd number in the tuple!")
}

To access the element of a tuple, we can use the index like this:

fn indexing_tuple() {
    let numbers = (1, 2, 3);
    // Replace below ??? with the tuple indexing syntax.
    let second = numbers.1;

    assert_eq!(2, second,
        "This is not the 2nd number in the tuple!")
}

Conclusion

The fourth chapter of Rustlings - Primitive type ends here.
TIL:

  • How to declare and use the primitive types
  • Working with array, tuple, string and some helpful methods to work with them

Thanks for reading and please add comments below if you have any questions