first go at the exercises

solutions/00_intro/intro1.rs

@@ -1,4 +1,5 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // Congratulations, you finished the first exercise 🎉
+    // As an introduction to Rustlings, the first exercise only required
+    // entering `n` in the terminal to go to the next exercise.
 }

solutions/00_intro/intro2.rs

@@ -1,4 +1,4 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // `println!` instead of `printline!`.
+    println!("Hello world!");
 }

solutions/01_variables/variables1.rs

@@ -1,4 +1,6 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // Declaring variables requires the `let` keyword.
+    let x = 5;
+
+    println!("x has the value {x}");
 }

solutions/01_variables/variables2.rs

@@ -1,4 +1,16 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // The easiest way to fix the compiler error is to initialize the
+    // variable `x`. By setting its value to an integer, Rust infers its type
+    // as `i32` which is the default type for integers.
+    let x = 42;
+
+    // But we can enforce a type different from the default `i32` by adding
+    // a type annotation:
+    // let x: u8 = 42;
+
+    if x == 10 {
+        println!("x is ten!");
+    } else {
+        println!("x is not ten!");
+    }
 }

solutions/01_variables/variables3.rs

@@ -1,4 +1,15 @@
+#![allow(clippy::needless_late_init)]
+
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // Reading uninitialized variables isn't allowed in Rust!
+    // Therefore, we need to assign a value first.
+    let x: i32 = 42;
+
+    println!("Number {x}");
+
+    // It is possible to declare a variable and initialize it later.
+    // But it can't be used before initialization.
+    let y: i32;
+    y = 42;
+    println!("Number {y}");
 }

solutions/01_variables/variables4.rs

@@ -1,4 +1,9 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // In Rust, variables are immutable by default.
+    // Adding the `mut` keyword after `let` makes the declared variable mutable.
+    let mut x = 3;
+    println!("Number {x}");
+
+    x = 5;
+    println!("Number {x}");
 }

solutions/01_variables/variables5.rs

@@ -1,4 +1,9 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    let number = "T-H-R-E-E";
+    println!("Spell a number: {}", number);
+
+    // Using variable shadowing
+    // https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html#shadowing
+    let number = 3;
+    println!("Number plus two is: {}", number + 2);
 }

solutions/01_variables/variables6.rs

@@ -1,4 +1,6 @@
+// The type of constants must always be annotated.
+const NUMBER: u64 = 3;
+
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    println!("Number: {NUMBER}");
 }

solutions/02_functions/functions1.rs

@@ -1,4 +1,8 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+// Some function with the name `call_me` without arguments or a return value.
+fn call_me() {
+    println!("Hello world!");
+}
+
+fn main() {
+    call_me();
 }

solutions/02_functions/functions2.rs

@@ -1,4 +1,11 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+// The type of function arguments must be annotated.
+// Added the type annotation `u64`.
+fn call_me(num: u64) {
+    for i in 0..num {
+        println!("Ring! Call number {}", i + 1);
+    }
+}
+
+fn main() {
+    call_me(3);
 }

solutions/02_functions/functions3.rs

@@ -1,4 +1,10 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn call_me(num: u8) {
+    for i in 0..num {
+        println!("Ring! Call number {}", i + 1);
+    }
+}
+
+fn main() {
+    // `call_me` expects an argument.
+    call_me(5);
 }

solutions/02_functions/functions4.rs

@@ -1,4 +1,17 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn is_even(num: i64) -> bool {
+    num % 2 == 0
+}
+
+// The return type must always be annotated.
+fn sale_price(price: i64) -> i64 {
+    if is_even(price) {
+        price - 10
+    } else {
+        price - 3
+    }
+}
+
+fn main() {
+    let original_price = 51;
+    println!("Your sale price is {}", sale_price(original_price));
 }

solutions/02_functions/functions5.rs

@@ -1,4 +1,9 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn square(num: i32) -> i32 {
+    // Removed the semicolon `;` at the end of the line below to implicitly return the result.
+    num * num
+}
+
+fn main() {
+    let answer = square(3);
+    println!("The square of 3 is {answer}");
 }

solutions/03_if/if1.rs

@@ -1,4 +1,32 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn bigger(a: i32, b: i32) -> i32 {
+    if a > b {
+        a
+    } else {
+        b
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+// Don't mind this for now :)
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ten_is_bigger_than_eight() {
+        assert_eq!(10, bigger(10, 8));
+    }
+
+    #[test]
+    fn fortytwo_is_bigger_than_thirtytwo() {
+        assert_eq!(42, bigger(32, 42));
+    }
+
+    #[test]
+    fn equal_numbers() {
+        assert_eq!(42, bigger(42, 42));
+    }
 }

solutions/03_if/if2.rs

@@ -1,4 +1,33 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn foo_if_fizz(fizzish: &str) -> &str {
+    if fizzish == "fizz" {
+        "foo"
+    } else if fizzish == "fuzz" {
+        "bar"
+    } else {
+        "baz"
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn foo_for_fizz() {
+        assert_eq!(foo_if_fizz("fizz"), "foo");
+    }
+
+    #[test]
+    fn bar_for_fuzz() {
+        assert_eq!(foo_if_fizz("fuzz"), "bar");
+    }
+
+    #[test]
+    fn default_to_baz() {
+        assert_eq!(foo_if_fizz("literally anything"), "baz");
+    }
 }

solutions/03_if/if3.rs

@@ -1,4 +1,53 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+fn animal_habitat(animal: &str) -> &str {
+    let identifier = if animal == "crab" {
+        1
+    } else if animal == "gopher" {
+        2
+    } else if animal == "snake" {
+        3
+    } else {
+        // Any unused identifier.
+        4
+    };
+
+    // Instead of such an identifier, you would use an enum in Rust.
+    // But we didn't get into enums yet.
+    if identifier == 1 {
+        "Beach"
+    } else if identifier == 2 {
+        "Burrow"
+    } else if identifier == 3 {
+        "Desert"
+    } else {
+        "Unknown"
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn gopher_lives_in_burrow() {
+        assert_eq!(animal_habitat("gopher"), "Burrow")
+    }
+
+    #[test]
+    fn snake_lives_in_desert() {
+        assert_eq!(animal_habitat("snake"), "Desert")
+    }
+
+    #[test]
+    fn crab_lives_on_beach() {
+        assert_eq!(animal_habitat("crab"), "Beach")
+    }
+
+    #[test]
+    fn unknown_animal() {
+        assert_eq!(animal_habitat("dinosaur"), "Unknown")
+    }
 }

solutions/04_primitive_types/primitive_types1.rs

@@ -1,4 +1,11 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    let is_morning = true;
+    if is_morning {
+        println!("Good morning!");
+    }
+
+    let is_evening = !is_morning;
+    if is_evening {
+        println!("Good evening!");
+    }
 }

solutions/04_primitive_types/primitive_types2.rs

@@ -1,4 +1,21 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    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!");
+    }
+
+    // Example with an emoji.
+    let your_character = '🦀';
+
+    if your_character.is_alphabetic() {
+        println!("Alphabetical!");
+    } else if your_character.is_numeric() {
+        println!("Numerical!");
+    } else {
+        println!("Neither alphabetic nor numeric!");
+    }
 }

solutions/04_primitive_types/primitive_types3.rs

@@ -1,4 +1,11 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // An array with 100 elements of the value 42.
+    let a = [42; 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");
+    }
 }

solutions/04_primitive_types/primitive_types4.rs

@@ -1,4 +1,23 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn slice_out_of_array() {
+        let a = [1, 2, 3, 4, 5];
+        //       0  1  2  3  4  <- indices
+        //          -------
+        //             |
+        //             +--- slice
+
+        // Note that the upper index 4 is excluded.
+        let nice_slice = &a[1..4];
+        assert_eq!([2, 3, 4], nice_slice);
+
+        // The upper index can be included by using the syntax `..=` (with `=` sign)
+        let nice_slice = &a[1..=3];
+        assert_eq!([2, 3, 4], nice_slice);
+    }
 }

solutions/04_primitive_types/primitive_types5.rs

@@ -1,4 +1,8 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    let cat = ("Furry McFurson", 3.5);
+
+    // Destructuring the tuple.
+    let (name, age) = cat;
+
+    println!("{name} is {age} years old");
 }

solutions/04_primitive_types/primitive_types6.rs

@@ -1,4 +1,16 @@
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn indexing_tuple() {
+        let numbers = (1, 2, 3);
+
+        // Tuple indexing syntax.
+        let second = numbers.1;
+
+        assert_eq!(second, 2, "This is not the 2nd number in the tuple!");
+    }
 }

solutions/quizzes/quiz1.rs

@@ -1,4 +1,30 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+// Mary is buying apples. The price of an apple is calculated as follows:
+// - An apple costs 2 rustbucks.
+// - However, if Mary buys more than 40 apples, the price of each apple in the
+// entire order is reduced to only 1 rustbuck!
+
+fn calculate_price_of_apples(n_apples: u64) -> u64 {
+    if n_apples > 40 {
+        n_apples
+    } else {
+        2 * n_apples
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+// Don't change the tests!
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn verify_test() {
+        assert_eq!(calculate_price_of_apples(35), 70);
+        assert_eq!(calculate_price_of_apples(40), 80);
+        assert_eq!(calculate_price_of_apples(41), 41);
+        assert_eq!(calculate_price_of_apples(65), 65);
+    }
 }