Add more examples for countdown (#183)

03_recursion/rust/02_countdown/main.rs

@@ -0,0 +1,52 @@
+// Rust has three kinds of loops: loop, while, and for. Let’s try each one + recursive.
+fn main() {
+    countdown_loop(5);
+    println!("------");
+
+    countdown_while(5);
+    println!("------");
+
+    countdown_for(5);
+    println!("------");
+
+    countdown_recursive(5);
+}
+
+
+fn countdown_loop(count: usize) {
+    let mut i = count;
+
+    loop {
+        println!("{}", i);
+        i -= 1;
+
+        if i <= 0 {
+            break;
+        }
+    }
+}
+
+fn countdown_while(count: usize) {
+    let mut i = count;
+
+    while i > 0 {
+        println!("{}", i);
+
+        i -= 1;
+    }
+}
+
+
+fn countdown_for(count: usize) {
+    for i in (1..count + 1).rev() {
+        println!("{}", i);
+    }
+}
+
+fn countdown_recursive(count: usize) {
+    println!("{}", count);
+
+    if count > 1 {
+        return countdown_recursive(count - 1);
+    }
+}