4 files changed, 103 insertions, 8 deletions
diff --git a/rustlings/solutions/09_strings/strings1.rs b/rustlings/solutions/09_strings/strings1.rs
index dcf2377..f7ba811 100644
--- a/rustlings/solutions/09_strings/strings1.rs
+++ b/rustlings/solutions/09_strings/strings1.rs
@@ -1,4 +1,9 @@
+fn current_favorite_color() -> String {
+    // Equivalent to `String::from("blue")`
+    "blue".to_string()
+}
+
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    let answer = current_favorite_color();
+    println!("My current favorite color is {answer}");
 }
diff --git a/rustlings/solutions/09_strings/strings2.rs b/rustlings/solutions/09_strings/strings2.rs
index dcf2377..7de311f 100644
--- a/rustlings/solutions/09_strings/strings2.rs
+++ b/rustlings/solutions/09_strings/strings2.rs
@@ -1,4 +1,15 @@
+fn is_a_color_word(attempt: &str) -> bool {
+    attempt == "green" || attempt == "blue" || attempt == "red"
+}
+
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    let word = String::from("green");
+
+    if is_a_color_word(&word) {
+        //             ^ added to have `&String` which is automatically
+        //               coerced to `&str` by the compiler.
+        println!("That is a color word I know!");
+    } else {
+        println!("That is not a color word I know.");
+    }
 }
diff --git a/rustlings/solutions/09_strings/strings3.rs b/rustlings/solutions/09_strings/strings3.rs
index dcf2377..ee6b56a 100644
--- a/rustlings/solutions/09_strings/strings3.rs
+++ b/rustlings/solutions/09_strings/strings3.rs
@@ -1,4 +1,49 @@
+fn trim_me(input: &str) -> &str {
+    input.trim()
+}
+
+fn compose_me(input: &str) -> String {
+    // The macro `format!` has the same syntax as `println!`, but it returns a
+    // string instead of printing it to the terminal.
+    // Equivalent to `input.to_string() + " world!"`
+    format!("{input} world!")
+}
+
+fn replace_me(input: &str) -> String {
+    input.replace("cars", "balloons")
+}
+
 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 {
+    use super::*;
+
+    #[test]
+    fn trim_a_string() {
+        assert_eq!(trim_me("Hello!     "), "Hello!");
+        assert_eq!(trim_me("  What's up!"), "What's up!");
+        assert_eq!(trim_me("   Hola!  "), "Hola!");
+        assert_eq!(trim_me("Hi!"), "Hi!");
+    }
+
+    #[test]
+    fn compose_a_string() {
+        assert_eq!(compose_me("Hello"), "Hello world!");
+        assert_eq!(compose_me("Goodbye"), "Goodbye world!");
+    }
+
+    #[test]
+    fn replace_a_string() {
+        assert_eq!(
+            replace_me("I think cars are cool"),
+            "I think balloons are cool",
+        );
+        assert_eq!(
+            replace_me("I love to look at cars"),
+            "I love to look at balloons",
+        );
+    }
 }
diff --git a/rustlings/solutions/09_strings/strings4.rs b/rustlings/solutions/09_strings/strings4.rs
index dcf2377..3c69b97 100644
--- a/rustlings/solutions/09_strings/strings4.rs
+++ b/rustlings/solutions/09_strings/strings4.rs
@@ -1,4 +1,38 @@
+fn string_slice(arg: &str) {
+    println!("{arg}");
+}
+
+fn string(arg: String) {
+    println!("{arg}");
+}
+
 fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+    string_slice("blue");
+
+    string("red".to_string());
+
+    string(String::from("hi"));
+
+    string("rust is fun!".to_owned());
+
+    // Here, both answers work.
+    // `.into()` converts a type into an expected type.
+    // If it is called where `String` is expected, it will convert `&str` to `String`.
+    string("nice weather".into());
+    // But if it is called where `&str` is expected, then `&str` is kept `&str` since no conversion is needed.
+    // If you remove the `#[allow(…)]` line, then Clippy will tell you to remove `.into()` below since it is a useless conversion.
+    #[allow(clippy::useless_conversion)]
+    string_slice("nice weather".into());
+
+    string(format!("Interpolation {}", "Station"));
+
+    // WARNING: This is byte indexing, not character indexing.
+    // Character indexing can be done using `s.chars().nth(INDEX)`.
+    string_slice(&String::from("abc")[0..1]);
+
+    string_slice("  hello there ".trim());
+
+    string("Happy Monday!".replace("Mon", "Tues"));
+
+    string("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }