Add some exercises about Strings and &strs!

README.md

@@ -39,6 +39,15 @@ If you need more help or would like to compare solutions, you can ask in [#rust
 - ["primitive_types1.rs"](http://play.rust-lang.org/?code=%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Booleans+%28%60bool%60%29%0A%0A++++let+is_morning+%3D+true%3B%0A++++if+is_morning+%7B%0A++++++++println%21%28%22Good+morning%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+the+rest+of+this+line+like+the+example%21+Or+make+it+be+false%21%0A++++if+is_evening+%7B%0A++++++++println%21%28%22Good+evening%21%22%29%3B%0A++++%7D%0A%7D%0A)
 - ["primitive_types2.rs"](http://play.rust-lang.org/?code=%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Characters+%28%60char%60%29%0A%0A++++let+my_first_initial+%3D+%27C%27%3B%0A++++if+my_first_initial.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+my_first_initial.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+this+line+like+the+example%21+What%27s+your+favorite+character%3F%0A++++%2F%2F+Try+a+letter%2C+try+a+number%2C+try+a+special+character%2C+try+a+character%0A++++%2F%2F+from+a+different+language+than+your+own%2C+try+an+emoji%21%0A++++if+your_character.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+your_character.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%7D%0A)
 
+### Strings
+
+[Relevant chapter in The Rust Programming Language](https://doc.rust-lang.org/stable/book/strings.html)
+
+- ["strings1.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile+without+changing+the+function+signature%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+answer+%3D+current_favorite_color%28%29%3B%0A++++println%21%28%22My+current+favorite+color+is+%7B%7D%22%2C+answer%29%3B%0A%7D%0A%0Afn+current_favorite_color%28%29+-%3E+String+%7B%0A++++%22blue%22%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+The+%60current_favorite_color%60+function+is+currently+returning+a+string+slice+with+the+%60%27static%60%0A%2F%2F+lifetime.+We+know+this+because+the+data+of+the+string+lives+in+our+code+itself+--+it+doesn%27t%0A%2F%2F+come+from+a+file+or+user+input+or+another+program+--+so+it+will+live+as+long+as+our+program%0A%2F%2F+lives.+But+it+is+still+a+string+slice.+There%27s+one+way+to+create+a+%60String%60+by+converting+a%0A%2F%2F+string+slice+covered+in+the+Strings+chapter+of+the+book%2C+and+another+way+that+uses+the+%60From%60%0A%2F%2F+trait.%0A)
+- ["strings2.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile+without+changing+the+function+signature%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+guess1+%3D+%22blue%22.to_string%28%29%3B+%2F%2F+Try+not+changing+this+line+%3A%29%0A++++let+correct+%3D+guess_favorite_color%28guess1%29%3B%0A++++if+correct+%7B%0A++++++++println%21%28%22You+guessed+correctly%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Nope%2C+that%27s+not+it.%22%29%3B%0A++++%7D%0A%7D%0A%0Afn+guess_favorite_color%28attempt%3A+%26str%29+-%3E+bool+%7B%0A++++attempt+%3D%3D+%22green%22%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Yes%2C+it+would+be+really+easy+to+fix+this+by+just+changing+the+value+bound+to+%60guess1%60+to+be+a%0A%2F%2F+string+slice+instead+of+a+%60String%60%2C+wouldn%27t+it%3F%3F+There+is+a+way+to+add+one+character+to+line%0A%2F%2F+5%2C+though%2C+that+will+coerce+the+%60String%60+into+a+string+slice.%0A)
+- ["strings3.rs"](http://play.rust-lang.org/?code=%2F%2F+Ok%2C+here+are+a+bunch+of+values--+some+are+%60Strings%60%2C+some+are+%60%26strs%60.+Your%0A%2F%2F+task+is+to+call+one+of+these+two+functions+on+each+value+depending+on+what%0A%2F%2F+you+think+each+value+is.+That+is%2C+add+either+%60string_slice%60+or+%60string%60%0A%2F%2F+before+the+parentheses+on+each+line.+If+you%27re+right%2C+it+will+compile%21%0A%0Afn+string_slice%28arg%3A+%26str%29+%7B+println%21%28%22%7B%7D%22%2C+arg%29%3B+%7D%0Afn+string%28arg%3A+String%29+%7B+println%21%28%22%7B%7D%22%2C+arg%29%3B+%7D%0A%0Afn+main%28%29+%7B%0A++++%28%22blue%22%29%3B%0A++++%28%22red%22.to_string%28%29%29%3B%0A++++%28String%3A%3Afrom%28%22hi%22%29%29%3B%0A++++%28format%21%28%22Interpolation+%7B%7D%22%2C+%22Station%22%29%29%3B%0A++++%28%26String%3A%3Afrom%28%22abc%22%29%5B0..1%5D%29%3B%0A++++%28%22++hello+there+%22.trim%28%29%29%3B%0A++++%28%22Happy+Monday%21%22.to_string%28%29.replace%28%22Mon%22%2C+%22Tues%22%29%29%3B%0A++++%28%22mY+sHiFt+KeY+iS+sTiCkY%22.to_lowercase%28%29%29%3B%0A%7D%0A)
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+
 ### Modules
 
 [Relevant chapter in The Rust Programming Language](https://doc.rust-lang.org/stable/book/crates-and-modules.html)

strings/strings1.rs

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+// Make me compile without changing the function signature! Scroll down for hints :)
+
+fn main() {
+    let answer = current_favorite_color();
+    println!("My current favorite color is {}", answer);
+}
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+fn current_favorite_color() -> String {
+    "blue"
+}
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+// The `current_favorite_color` function is currently returning a string slice with the `'static`
+// lifetime. We know this because the data of the string lives in our code itself -- it doesn't
+// come from a file or user input or another program -- so it will live as long as our program
+// lives. But it is still a string slice. There's one way to create a `String` by converting a
+// string slice covered in the Strings chapter of the book, and another way that uses the `From`
+// trait.

strings/strings2.rs

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+// Make me compile without changing the function signature! Scroll down for hints :)
+
+fn main() {
+    let guess1 = "blue".to_string(); // Try not changing this line :)
+    let correct = guess_favorite_color(guess1);
+    if correct {
+        println!("You guessed correctly!");
+    } else {
+        println!("Nope, that's not it.");
+    }
+}
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+fn guess_favorite_color(attempt: &str) -> bool {
+    attempt == "green"
+}
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+// Yes, it would be really easy to fix this by just changing the value bound to `guess1` to be a
+// string slice instead of a `String`, wouldn't it?? There is a way to add one character to line
+// 5, though, that will coerce the `String` into a string slice.

strings/strings3.rs

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+// Ok, here are a bunch of values-- some are `Strings`, some are `&strs`. Your
+// task is to call one of these two functions on each value depending on what
+// you think each value is. That is, add either `string_slice` or `string`
+// before the parentheses on each line. If you're right, it will compile!
+
+fn string_slice(arg: &str) { println!("{}", arg); }
+fn string(arg: String) { println!("{}", arg); }
+
+fn main() {
+    ("blue");
+    ("red".to_string());
+    (String::from("hi"));
+    (format!("Interpolation {}", "Station"));
+    (&String::from("abc")[0..1]);
+    ("  hello there ".trim());
+    ("Happy Monday!".to_string().replace("Mon", "Tues"));
+    ("mY sHiFt KeY iS sTiCkY".to_lowercase());
+}