Reading input

Read the user's guess with std::io::stdin.

Reading input

To read a line from the user, an empty String is created and passed to read_line as &mut. The \n at the end of the line is added to the text too:

let mut tahmin = String::new();
io::stdin()
    .read_line(&mut tahmin)
    .expect("Satır okunamadı");
println!("Tahminin: {}", tahmin.trim());

read_line returns an io::Result<usize> (the number of bytes read); expect stops the program with a message on error.

Why &mut and appending?

read_line appends text; it doesn't overwrite. If you reuse the same String in a loop, call tahmin.clear() every round. In the exercises of these lessons we'll use a fixed text instead of input; the same trim and parse steps apply to real input.

let mut tahmin = String::new();
tahmin.push_str("12\n");
tahmin.clear();
tahmin.push_str("34\n");
println!("{}", tahmin.trim());   // 34

Exercise Clean the input

Clean the text let girdi = String::from(" 42\n");, which stands for user input, with trim and print it as Tahmin: 42.

Show example solution

fn main() {
    let girdi = String::from("  42\n");
    let t = girdi.trim();
    println!("Tahmin: {}", t);
}

Test yourself

If the user types <code>42</code> and presses Enter, what does <code>tahmin</code> contain?
- Empty text
- "42\n" ("42\r\n" on Windows)
- The number 42
- "42"
Show answer

"42\n" ("42\r\n" on Windows) — read_line appends the line ending too; trim cleans it up.

Read the line

let mut tahmin = String::new();
io::stdin()
    .read_line(____)
    .expect("Satır okunamadı");

Show answer

let mut tahmin = String::new();
io::stdin()
    .read_line(&mut tahmin)
    .expect("Satır okunamadı");

Piece and its role

io::stdin()

Standard input
read_line

Appends a line
expect

Stops on error
trim()

Removes spaces and \n

Next lesson: Comparing numbers

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