fibo.rs

use std::io;
use std::io::Write;

fn fibo(n:u32) -> u32 {
  if n <= 2 {
    1
  } else {
    let mut prev1 = 1;
    let mut prev2 = 1;
    for _n in 2..n {
      let next = prev1 + prev2;
      prev2 = prev1;
      prev1 = next;
    }
    prev1
  }
}


fn main() {
  let mut s;
  let num : u32 = loop {
    print!("Enter a number: ");
    io::stdout().flush()
      .expect("Failed to flush stdout");

    s = String::new();
    io::stdin().read_line(&mut s)
      .expect("Failed to read line");

    s = s.trim().to_string();
    if s.len() == 0 {
      println!("");
      std::process::exit(1);
    }

    let _ : u32 = match s.parse() {
      Ok(val) => {
        break val;
      },
      Err(_) => {
        println!("Bad num: {}", s);
        continue;
      },
    };
  };

  println!("{}-th Fibonacci number is: {}",
    num,
    fibo(num)
  );
}