Add external dep for rand

rustbook/guessing_game/Cargo.toml

@@ -4,3 +4,4 @@ version = "0.1.0"
 authors = ["Dan Buch <daniel.buch@gmail.com>"]
 
 [dependencies]
+rand = "0.4.0"

rustbook/guessing_game/src/main.rs

@@ -1,3 +1,14 @@
+use std::io;
+
 fn main() {
-    println!("Hello, world!");
+    println!("Guess the number!");
+
+    println!("Please input your guess.");
+
+    let mut guess = String::new();
+
+    io::stdin().read_line(&mut guess)
+        .expect("Failed to read line");
+
+    println!("You guessed: {}", guess);
 }