[Exercise] - Adding fibonacci program

fib/main.rs

@@ -0,0 +1,22 @@
+const GOLDEN_RATIO:f32 = 1.6180339887;
+const GOLDEN_CONJUGATE:f32 = -0.6180339887;
+const FIVE_SQRT:f32 = 2.236067977;//√5
+fn fib(n:f32) -> f32 {
+    return (GOLDEN_RATIO.powf(n) - GOLDEN_CONJUGATE.powf(n)) / FIVE_SQRT;
+}
+fn main(){
+    let args: Vec<String> = std::env::args().collect();
+    let input = args.get(1);
+    match input {
+        Some (inStr) => {
+            match inStr.trim().parse() {
+                Ok (n) => {
+                    let result = fib(n);
+                    println!("fib({}) = {:.2}",n,result);
+                },
+                Err(err) => println!("can't parse value to float: {}",err)
+            }
+        },
+        None => println!("fib [LIMIT]")
+    };
+}