Do the fibs

variables/src/main.rs

@@ -18,11 +18,24 @@ fn main() {
     match command.as_str() {
         "tc" => {
             if command_args.len() < 1 {
-                println!("ERROR: missing a value to convert");
+                eprintln!("ERROR: missing a value to convert");
                 process::exit(1);
             }
             temp_convert(command_args[0].as_str().to_string())
         }
+        "fib" => {
+            if command_args.len() < 1 {
+                eprintln!("ERROR: missing a value to fib");
+                process::exit(1);
+            }
+            let n: u64 = command_args[0]
+                .parse()
+                .expect("could not parse value to fib");
+            if n >= 40 {
+                eprintln!("WARN: this might take a while");
+            }
+            fib_n(n)
+        }
         "rx" => redefine_x(),
         "help" | _ => show_help(),
     }
@@ -32,6 +45,7 @@ fn show_help() {
     println!("Usage: variables <command> [command_args]");
     println!();
     println!("The value for <command> may be one of:");
+    println!("  fib - generate Nth Fibonacci number");
     println!("  tc  - convert temperatures between Fahrenheit and Celsius");
     println!("  rx  - redefine x");
     println!();
@@ -59,7 +73,7 @@ fn temp_convert(to_convert: String) {
             .expect("failed to parse temperature");
         println!("{}C", temp_convert_f2c(f));
     } else {
-        println!("What are we supposed to do to {:?}?", to_convert);
+        eprintln!("ERROR: What are we supposed to do to {:?}?", to_convert);
     }
 }
 
@@ -70,3 +84,15 @@ fn temp_convert_c2f(c: f32) -> f32 {
 fn temp_convert_f2c(f: f32) -> f32 {
     (f - 32.0) * (5.0 / 9.0)
 }
+
+fn fib_n(n: u64) {
+    println!("{}", fib_up_to(n));
+}
+
+fn fib_up_to(n: u64) -> u64 {
+    match n {
+        0 => 0,
+        1 => 1,
+        _ => fib_up_to(n - 1) + fib_up_to(n - 2),
+    }
+}