Testing const fn

const.rs

@@ -0,0 +1,20 @@
+use std::io::stdin;
+
+const fn double(x: i32) -> i32 {
+    x * 2
+}
+
+const FIVE: i32 = 5;
+const TEN: i32 = double(FIVE);
+
+fn main() {
+    assert_eq!(5, FIVE);
+    assert_eq!(10, double(FIVE));
+
+    println!("Your const is {}", double(10));
+
+    let mut s = String::new();
+    stdin().read_line(&mut s).unwrap();
+
+    println!("Your double: {}", double(s.trim().parse::<i32>().unwrap()));
+}