CODEWITHSUNDEEP
rustuser-input
Karelisho
Karelisho

Reputation: 28

User input always true using the .is_ok functions

How can I read from the console and avoid crashing if the user presses enter without entering anything?

let mut objectnumber = String::new();
println!("mennyi súlyt szeretnél megnézni? 3.=255 int");
if io::stdin().read_line(&mut objectnumber).is_ok() {
   println!("{}csdcds", objectnumber);
}

//panic!("{}",objectnumber.len());
if objectnumber.len() < 3 {
   let localrandnum: u8 = thread_rng().gen_range(0..=255);
   println!("miután nem adtál meg semmit sem ezért {localrandnum}.at írtam be neked");
   objectnumber = localrandnum.to_string();
}
let objectnumber: u8 = objectnumber.trim().parse::<u8>().expect("null");

This is working but I don't think it should be done like this in Rust. I don't know why is it ok even on empty line while the parse is talking about it being empty.

Upvotes: 0

Views: 105

Answers (1)

Finomnis
Finomnis

Reputation: 22476

Fixes I made:

  • read_line returns a Result indicating whether or not there was an error reading from stdin. Usually this only happens in very specific circumstances, so let's just unwrap this for now.
  • objectnumber.len() gives you the length of the string, not its content. To check its content for < 3, we need to parse() it to a u8 first.
  • Don't expect the parse, because this one depends on user input. Do a proper error handling instead. This is the point that will tell you if the number is >255, <0 or something else entirely. Let's for now just default to '0', because it will then get caught by the < 3.
  • Don't convert the number you generated with the thread_rng to a String; instead, write it to objectnumber directly. There is no point in converting it to a String and back.
use std::io;

use rand::{thread_rng, Rng};

fn main() {
    let mut objectnumber = String::new();
    println!("mennyi súlyt szeretnél megnézni? 3.=255 int");
    io::stdin()
        .read_line(&mut objectnumber)
        .expect("Unable to read from stdin!");

    // Convert from String to u8
    let mut objectnumber: u8 = objectnumber.trim().parse::<u8>().unwrap_or(0);

    if objectnumber < 3 {
        objectnumber = thread_rng().gen_range(0..=255);
        println!("miután nem adtál meg semmit sem ezért {objectnumber}.at írtam be neked");
    }

    println!("objectnumber: {}", objectnumber);
}

mennyi súlyt szeretnél megnézni? 3.=255 int
33
objectnumber: 33

mennyi súlyt szeretnél megnézni? 3.=255 int
1
miután nem adtál meg semmit sem ezért 191.at írtam be neked
objectnumber: 191

Upvotes: 2

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