Module 4Reading Input (stdin)Lesson 4 of 2322 min

stdin Basics: lines & tokens

read_line, split_whitespace, parse — real stdin vs playground simulation.

Real interview / CP style (local)

rust

use std::io::{self, BufRead};

fn main() {
    let stdin = io::stdin();
    let mut lines = stdin.lock().lines();
    let n: usize = lines.next().unwrap().unwrap().trim().parse().unwrap();
    // ...
}

Playground / tests: simulate input with a string

Online runners here often have empty stdin, so we practice the same parsing logic on a string:

rust

let input = "3\n1 2 3\nhello world\n";
for line in input.lines() { ... }

Tokens

rust

let nums: Vec<i32> = line
    .split_whitespace()
    .map(|t| t.parse().unwrap())
    .collect();

Tips

Always trim() before parse

Prefer collecting all tokens if format varies

In production, handle Result instead of unwrap

Challenge

Parse safely with Result instead of unwrap for a bad token "x".

Tips

trim before parse
split_whitespace handles multi-spaces
Simulate stdin with string.lines() here

Try it live

stdin Basics: lines & tokensRust 2021

Loading editor…

Output

Press Run to compile and execute.