Add solutions to intro and variables

solutions/00_intro/intro1.rs

@@ -1 +1,2 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// The exercise `intro1` only requires entering `n` in the terminal to go to the next exercise.
+// It is just an introduction to how Rustlings works.

solutions/00_intro/intro2.rs

@@ -1 +1,4 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    // `println!` instead of `printline!`.
+    println!("Hello world!");
+}

solutions/01_variables/variables1.rs

@@ -1 +1,6 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    // Declaring variables requires the `let` keyword.
+    let x = 5;
+
+    println!("x has the value {x}");
+}

solutions/01_variables/variables2.rs

@@ -1 +1,16 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    // 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 +1,13 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    // Reading uninitialized variables isn't allowed in Rust!
+    // Therefore, we need to assign a value first.
+    let x: i32 = 42;
+
+    println!("Number {x}");
+
+    // It 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 +1,9 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    // 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; // Don't change this line
+    println!("Number {x}");
+}

solutions/01_variables/variables5.rs

@@ -1 +1,9 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+fn main() {
+    let number = "T-H-R-E-E"; // Don't change this line
+    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 +1,6 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// The type of constants must always be annotated.
+const NUMBER: u64 = 3;
+
+fn main() {
+    println!("Number: {NUMBER}");
+}